Challenging Brain Teasers

Easy Brain Teasers

1. I’m tall when I’m young, and I’m short when I’m old. What am I?
   Answer: A candle.
2. What has to be broken before you can use it?
   Answer: An egg.
3. What has a heart that doesn’t beat?
   Answer: An artichoke.
4. What comes once in a minute, twice in a moment, but never in a thousand years?
   Answer: The letter M.
5. What has many teeth but can’t bite?
   Answer: A comb.
6. If two’s company, and three’s a crowd, what are four and five?
   Answer: Nine.
7. I am an odd number. Take away one letter, and I become even. What am I?
   Answer: Seven (remove the “s”).
8. What number comes next in this sequence: 2, 6, 12, 20, 30, …?
   Answer: 42 (Add consecutive even numbers: +4, +6, +8, etc.).
9. The ages of a father and son add up to 66. The father’s age is the son’s age reversed. What are their ages?
   Answer: 51 and 15, or 42 and 24, or 60 and 06.
10. What is half of two plus two?
    Answer: Three (½ of 2 = 1, and 1 + 2 = 3).

11. Using only addition, how do you add eight 8’s to get 1,000?
    Answer: 888 + 88 + 8 + 8 + 8 = 1,000.
12. If you multiply me by any other number, the answer will always be the same. What number am I?
    Answer: Zero.
13. I add six to eleven and get five. How is this possible?
    Answer: On a clock, 11 o’clock + 6 hours = 5 o’clock.
14. How many times can you subtract 10 from 100?
    Answer: Once (after subtracting 10, it’s no longer 100).
15. What is the sum of the first 10 positive integers?
    Answer: 55 (1 + 2 + 3 + … + 10 = 55).
16. If you have four apples and you take away three, how many do you have?
    Answer: Three (the ones you took).
17. What comes after 1, 4, 9, 16, 25, …?
    Answer: 36 (Squares of integers: 1², 2², 3², etc.).
18. How many times does the digit 9 appear between 1 and 100?
    Answer: 20.
19. A triangle has sides 3 cm, 4 cm, and 5 cm. What kind of triangle is it?
    Answer: Right triangle.
20. How many minutes are in 12 hours?
    Answer: 720 minutes.

21. What’s the probability of flipping a coin three times and it landing heads each time?
    Answer: 1/8.
22. I am a number. Multiply me by 4, then subtract 6, and you’ll get 30. What am I?
    Answer: 9.
23. Divide 30 by ½ and add 10. What do you get?
    Answer: 70.
24. What three positive numbers give the same result when multiplied and added together?
    Answer: 1, 2, and 3.
25. What is the smallest positive number that is divisible by 2, 3, and 5?
    Answer: 30.
26. What’s 15% of 200?
    Answer: 30.
27. What’s 2 raised to the power of 5 (2⁵)?
    Answer: 32.
28. What’s 3 times 3 times 3?
    Answer: 27.
29. How many degrees are in a circle?
    Answer: 360 degrees.
30. What’s the perimeter of a square with side length 8?
    Answer: 32 (8 × 4).

31. What’s the area of a rectangle with length 10 and width 5?
    Answer: 50 (10 × 5).
32. What’s the factorial of 4 (4!)?
    Answer: 24 (4 × 3 × 2 × 1).
33. A book has 100 pages. How many digits are used to number them?
    Answer: 192.
34. How can you write 23 using only the number 2 five times?
    Answer: (22 + 2) ÷ 2 = 23.
35. A room contains a barrel that weighs 200 pounds. What can you add to make it weigh 210 pounds?
    Answer: The word “ten.”
36. How many total legs do 3 cows, 2 chickens, and 4 pigs have?
    Answer: 36.
37. The sum of three consecutive numbers is 36. What are the numbers?
    Answer: 11, 12, 13.
38. If a bottle of soda costs $1.10, and the bottle costs $1 more than the soda, how much is the soda?
    Answer: $0.05.
39. How many squares are there on a chessboard?
    Answer: 204.
40. What number am I if I am 4 times the sum of my digits?
    Answer: 36.

41. What’s the cube root of 27?
    Answer: 3.
42. What’s the sum of the angles in a hexagon?
    Answer: 720 degrees.
43. If a dozen eggs cost $3.60, how much does one egg cost?
    Answer: $0.30.
44. What’s the next prime number after 7?
    Answer: 11.
45. If it takes 5 machines 5 minutes to make 5 widgets, how long would it take 100 machines to make 100 widgets?
    Answer: 5 minutes.
46. What has four legs in the morning, two in the afternoon, and three in the evening?
    Answer: A person.
47. How many faces does a cube have?
    Answer: Six.
48. What’s 9 times 8?
    Answer: 72.
49. What two numbers multiply to 48 and add to 14?
    Answer: 6 and 8.
50. What is 1 + 1 × 1 + 1?
    Answer: 3.

51. A train leaves the station at 7:00 AM traveling at 60 miles per hour. Another train leaves the same station at 8:00 AM traveling at 80 miles per hour. How far from the station will the second train catch up to the first?
    Answer: 240 miles (They meet after 4 hours).
52. If it takes 4 people 4 hours to paint 4 walls, how many hours will it take 8 people to paint 8 walls?
    Answer: 4 hours (same rate).
53. What two-digit number is equal to double the sum of its digits?
    Answer: 18 (1 + 8 = 9, and 9 × 2 = 18).
54. What three-digit number has a ones digit equal to the sum of its hundreds and tens digits, and its hundreds digit is twice its tens digit?
    Answer: 261.
55. If you arrange the numbers 1 to 9 in a square grid so that every row, column, and diagonal adds up to 15, what’s the number in the center?
    Answer: 5.
56. How many ways can you make 50 cents using only quarters, dimes, and nickels?
    Answer: Six (combinations like 2 quarters, 5 dimes, etc.).
57. You have a 3-gallon jug and a 5-gallon jug, and you need to measure exactly 4 gallons. How do you do it?
    Answer: Fill the 5-gallon jug, pour into the 3-gallon jug until full, leaving 2 gallons in the 5-gallon jug. Empty the 3-gallon jug, pour the 2 gallons into it, then refill the 5-gallon jug and pour into the 3-gallon jug until full, leaving exactly 4 gallons in the 5-gallon jug.
58. What is the smallest number that is divisible by both 6 and 9?
    Answer: 18.
59. If you double my age and subtract 10, you get 50. How old am I?
    Answer: 30.
60. What’s the square root of 196?
    Answer: 14.

61. If today is Monday, what day will it be 45 days from now?
    Answer: Wednesday (45 ÷ 7 = 6 weeks and 3 days, so add 3 days to Monday).
62. How many edges does a cube have?
    Answer: 12.
63. A palindrome reads the same forwards and backwards. What is the largest three-digit palindrome divisible by 3?
    Answer: 999.
64. What is the next number in the sequence: 1, 1, 2, 3, 5, 8, 13, …?
    Answer: 21 (Fibonacci sequence).
65. What’s the smallest positive number divisible by 2, 3, 4, and 5?
    Answer: 60.
66. If 4 cats catch 4 mice in 4 minutes, how many mice can 8 cats catch in 8 minutes?
    Answer: 16 mice.
67. What’s the sum of the interior angles of a pentagon?
    Answer: 540 degrees.
68. What’s the largest two-digit number divisible by both 4 and 5?
    Answer: 80.
69. I am a three-digit number. My tens digit is 5 more than my ones digit, and my hundreds digit is 8 less than my tens digit. What number am I?
    Answer: 194.
70. How many ways can you arrange the letters in the word “MATH”?
    Answer: 24 (4! = 4 × 3 × 2 × 1).

71. If you roll two dice, what’s the probability that the sum is 7?
    Answer: 6/36 or 1/6.
72. What’s 25% of 64?
    Answer: 16.
73. A group of people is standing in a circle. Starting at one person and counting every third person, who will be the last person standing if there are 10 people?
    Answer: Person 4 (Josephus problem).
74. What number is both a square and a cube?
    Answer: 64 (8² and 4³).
75. If the area of a square is 81 square units, what is the length of one side?
    Answer: 9 units.
76. I am a number. Multiply me by 3 and subtract 7 to get 14. What number am I?
    Answer: 7.
77. What’s the volume of a cube with side length 4?
    Answer: 64 cubic units (4 × 4 × 4).
78. If a pizza has 12 slices and 5 people share it equally, how many slices does each person get?
    Answer: 2 slices each, with 2 slices left over.
79. What is 10% of 500?
    Answer: 50.
80. If you save $2 every day, how much will you have saved in a non-leap year?
    Answer: $730 (365 × 2).

81. What’s the smallest prime number?
    Answer: 2.
82. I have three digits. My hundreds digit is three times my tens digit, and my tens digit is twice my ones digit. What number am I?
    Answer: 621.
83. A car travels 60 miles per hour for 2 hours and 30 miles per hour for 1 hour. What’s the average speed?
    Answer: 50 miles per hour (total distance = 150 miles, total time = 3 hours).
84. What’s the square of 15?
    Answer: 225.
85. What’s 2⁴ + 3³?
    Answer: 41 (16 + 27).
86. How many seconds are there in an hour?
    Answer: 3,600 seconds.
87. What’s the next number in the pattern: 1, 4, 9, 16, 25, 36, …?
    Answer: 49 (squares of integers).
88. What’s the greatest common divisor (GCD) of 24 and 36?
    Answer: 12.
89. If you eat ⅓ of a pizza and then ½ of the remaining pizza, what fraction of the whole pizza have you eaten?
    Answer: 5/6.
90. What’s the remainder when 29 is divided by 6?
    Answer: 5.

91. If a rectangle has a perimeter of 20 and one side is 6, what is the length of the other side?
    Answer: 4.
92. What is the product of the first 5 prime numbers?
    Answer: 2310 (2 × 3 × 5 × 7 × 11).
93. A farmer has 17 sheep. All but 9 run away. How many does he have left?
    Answer: 9.
94. How many diagonals are in a hexagon?
    Answer: 9.
95. What’s 15 × 15?
    Answer: 225.
96. A bag contains 3 red balls, 5 blue balls, and 2 green balls. What’s the probability of picking a blue ball?
    Answer: 5/10 or ½.
97. What’s the sum of the first 5 positive even numbers?
    Answer: 30 (2 + 4 + 6 + 8 + 10).
98. What’s the least common multiple (LCM) of 6 and 8?
    Answer: 24.
99. How many lines of symmetry does a regular hexagon have?
    Answer: 6.
100. What’s the value of 3! × 2²?
     Answer: 24.

Medium Level Brain Teasers

1. A number is doubled and then reduced by 12. The result is 36. What is the number?
   Answer: 24.
2. If you add my digits, you get 11. I’m a two-digit number, and the difference between my digits is 3. What number am I?
   Answer: 47.
3. A rectangle’s perimeter is 72 cm. If its length is twice its width, what are the dimensions?
   Answer: Length = 24 cm, Width = 12 cm.
4. I am a four-digit number. My thousands digit is 4, my hundreds digit is half of 8, and my tens and ones digits add up to 9. What number am I?
   Answer: 4254.
5. What three consecutive numbers add up to 60?
   Answer: 19, 20, 21.
6. You roll two dice. What’s the probability that their sum is 8?
   Answer: 5/36.
7. A triangle has sides 6 cm, 8 cm, and 10 cm. What type of triangle is it?
   Answer: A right triangle (Pythagorean triple).
8. How many integers between 1 and 100 are divisible by both 2 and 5?
   Answer: 10 (Multiples of 10).
9. What number comes next in the pattern: 3, 9, 27, 81, …?
   Answer: 243 (Multiply by 3 each time).
10. A train is traveling at 90 km/h. How long will it take to travel 135 km?
    Answer: 1.5 hours.

11. What is the sum of the first 15 positive odd numbers?
    Answer: 225 (n², where n = 15).
12. If a sphere’s radius is doubled, by what factor does its volume increase?
    Answer: 8 times (Volume scales with the cube of the radius).
13. A book costs $12.99. If a student buys 3 books, how much will they pay, including 5% tax?
    Answer: $40.87.
14. What is the value of 4! (4 factorial)?
    Answer: 24 (4 × 3 × 2 × 1).
15. How many diagonals are there in an octagon?
    Answer: 20.
16. If a pizza is divided into 8 slices and you eat ¾ of the pizza, how many slices did you eat?
    Answer: 6 slices.
17. A 10-meter ladder is leaning against a wall. The base is 6 meters from the wall. How high up does the ladder reach?
    Answer: 8 meters (Pythagorean theorem).
18. What’s the sum of the interior angles of a decagon?
    Answer: 1,440 degrees.
19. If you multiply me by 5 and subtract 7, you get 33. What number am I?
    Answer: 8.
20. A clock shows 3:15. What is the angle between the hour and minute hands?
    Answer: 7.5 degrees.

21. A jar contains red, blue, and green marbles: 5 red, 7 blue, and 8 green. What’s the probability of randomly picking a green marble?
    Answer: 8/20 or 2/5.
22. What is the smallest prime number greater than 50?
    Answer: 53.
23. You have $20 and want to buy pens for $1.50 each. How many pens can you buy, and how much change will you get?
    Answer: 13 pens, $0.50 change.
24. What number has 12 factors and is less than 50?
    Answer: 36.
25. How many perfect squares are there between 1 and 1000?
    Answer: 31 (Squares of integers 1 through 31).
26. A car travels 60 km in 1.5 hours. What is its average speed in km/h?
    Answer: 40 km/h.
27. How many two-digit numbers are divisible by 3?
    Answer: 30 (from 12 to 99).
28. If 5 pencils cost $1.25, how much do 12 pencils cost?
    Answer: $3.00.
29. What number is halfway between 17 and 43?
    Answer: 30.
30. If a cube’s surface area is 54 square cm, what is the length of one side?
    Answer: 3 cm.

31. A wheel rotates 15 times per second. How many rotations does it complete in 2 minutes?
    Answer: 1,800 rotations.
32. What is the next number in the pattern: 2, 6, 12, 20, 30, …?
    Answer: 42 (Add consecutive even numbers: +4, +6, +8, …).
33. What’s the LCM of 9 and 12?
    Answer: 36.
34. How many edges does a triangular prism have?
    Answer: 9.
35. A cube has a volume of 64 cubic units. What is its surface area?
    Answer: 96 square units.
36. What is the probability of flipping a coin three times and getting exactly two heads?
    Answer: 3/8.
37. If a triangle has angles measuring 40° and 70°, what is the measure of the third angle?
    Answer: 70°.
38. How many ways can you arrange the letters in the word “SCHOOL”?
    Answer: 720 (6!).
39. What is the sum of the first 20 multiples of 5?
    Answer: 1,050.
40. What is the square root of 121 plus the cube root of 27?
    Answer: 14 (11 + 3).

41. If you triple a number and subtract 15, you get 30. What is the number?
    Answer: 15.
42. How many faces does a dodecahedron have?
    Answer: 12.
43. If the sum of two numbers is 90 and one is twice the other, what are the numbers?
    Answer: 30 and 60.
44. What is the area of a circle with a radius of 7 cm? Use π≈3.14\pi \approx 3.14π≈3.14.
    Answer: 153.86 square cm.
45. A rectangular room is 8 m by 5 m. How much carpet is needed to cover the floor?
    Answer: 40 square meters.
46. If 5x = 20, what is the value of 3x?
    Answer: 12.
47. What is the smallest three-digit number divisible by both 4 and 6?
    Answer: 108.
48. What’s the next number in the pattern: 81, 64, 49, 36, …?
    Answer: 25 (descending perfect squares).
49. If the perimeter of an equilateral triangle is 45 cm, what is the length of one side?
    Answer: 15 cm.
50. A jar contains 18 marbles: 6 red, 7 blue, and 5 green. What is the probability of drawing a red marble?
    Answer: 6/18 or 1/3.

51. How many diagonals are there in a heptagon?
    Answer: 14.
52. If two numbers multiply to give 72 and one of the numbers is 9, what is the other number?
    Answer: 8.
53. What is the prime factorization of 60?
    Answer: 22×3×52^2 \times 3 \times 522×3×5.
54. What is the greatest common divisor (GCD) of 36 and 54?
    Answer: 18.
55. A farmer sells 12 dozen eggs. How many individual eggs did they sell?
    Answer: 144 eggs.
56. What is the 8th term in the sequence: 2, 4, 8, 16, …?
    Answer: 256 (powers of 2).
57. If 2x + 5 = 17, what is the value of x?
    Answer: 6.
58. What is the square root of 256?
    Answer: 16.
59. What fraction is equivalent to 0.125?
    Answer: 1/8.
60. A train travels 300 km in 5 hours. What is its average speed?
    Answer: 60 km/h.

61. How many triangles can be formed by connecting three vertices of a hexagon?
    Answer: 20.
62. What is the sum of the angles in a quadrilateral?
    Answer: 360 degrees.
63. The sum of two numbers is 45. Their difference is 15. What are the numbers?
    Answer: 30 and 15.
64. What is the volume of a cylinder with a radius of 3 cm and a height of 10 cm? Hint!: Approximately 3.14π≈3.14.
    Answer: 282.6 cubic cm.
65. What is the cube root of 729?
    Answer: 9.
66. A pizza is divided into 12 equal slices. If you eat ⅔ of the pizza, how many slices did you eat?
    Answer: 8 slices.
67. What is the value of 23+322^3 + 3^223+32?
    Answer: 17 (8 + 9).
68. A clock reads 6:20. What is the angle between the hour and minute hands?
    Answer: 50 degrees.
69. How many prime numbers are there between 1 and 30?
    Answer: 10.
70. If 60% of a number is 24, what is the number?
    Answer: 40.

71. A cone has a radius of 4 cm and a height of 9 cm. What is its volume? Use π≈3.14\pi \approx 3.14π≈3.14.
    Answer: 150.72 cubic cm.
72. What is the least common multiple (LCM) of 10 and 15?
    Answer: 30.
73. If the area of a square is 121 square cm, what is the perimeter?
    Answer: 44 cm.
74. A group of friends share a $96 bill equally. If each person pays $12, how many friends are there?
    Answer: 8 friends.
75. How many ways can you rearrange the letters in the word “MATH”?
    Answer: 24.
76. What is the remainder when 67 is divided by 6?
    Answer: 1.
77. A triangle has sides of lengths 7 cm, 24 cm, and 25 cm. Is it a right triangle?
    Answer: Yes (Pythagorean theorem: 72+242=2527^2 + 24^2 = 25^272+242=252).
78. How many factors does 48 have?
    Answer: 10 factors.
79. A school has 450 students. If 60% are girls, how many girls are there?
    Answer: 270 girls.
80. What is the probability of rolling a number greater than 4 on a standard six-sided die?
    Answer: 2/6 or 1/3.

81. What is the sum of all the interior angles of a 15-sided polygon?
    Answer: 2,340 degrees.
82. A rectangle’s length is 3 times its width. If the perimeter is 48 cm, what are the dimensions?
    Answer: Length = 18 cm, Width = 6 cm.
83. A cylinder has a radius of 5 cm and a height of 7 cm. What is its surface area? Use π≈3.14\pi \approx 3.14π≈3.14.
    Answer: 376.8 square cm.
84. If the sum of the digits of a number is 9 and the number is divisible by 9, what is the smallest such number?
    Answer: 9.
85. How many cubes with side length 1 cm can fit into a box that is 10 cm by 5 cm by 4 cm?
    Answer: 200 cubes.
86. A triangle has one angle of 90° and one angle of 45°. What is the measure of the third angle?
    Answer: 45°.
87. What is the smallest positive number divisible by both 8 and 12?
    Answer: 24.
88. What is the greatest common divisor (GCD) of 42 and 56?
    Answer: 14.
89. If the sum of two consecutive integers is 99, what are the integers?
    Answer: 49 and 50.
90. How many vertices does a rectangular prism have?
    Answer: 8.

91. A triangle has side lengths of 9 cm, 12 cm, and 15 cm. What type of triangle is it?
    Answer: A right triangle (Pythagorean triple).
92. What is the square of 19?
    Answer: 361.
93. What is the cube of 6?
    Answer: 216.
94. What’s the next number in the pattern: 5, 25, 125, 625, …?
    Answer: 3,125 (Multiply by 5 each time).
95. If you flip a coin 3 times, what is the probability of getting exactly 1 head?
    Answer: 3/8.
96. A bag contains 3 red balls, 5 blue balls, and 2 green balls. What’s the probability of not picking a blue ball?
    Answer: 5/10 or 1/2.
97. How many edges does a pentagonal prism have?
    Answer: 15.
98. What is the value of 72−427^2 – 4^272−42?
    Answer: 33.
99. What’s the sum of the first 12 multiples of 3?
    Answer: 234.

Hard Brain Teasers– Coming Soon!