Brain Teasers: Can You Beat the Trick?: questions and answers
Study every question with its correct answer and explanation.
1. A bat and a ball cost $110 in total. The bat costs $100 more than the ball. How much does the ball cost?
- A. $10
- B. $5
- C. $1
- D. $15
Answer: $5
If the ball costs $5, the bat costs $105, and together they make $110. The instinctive answer of $10 would make the bat only $90 more than the ball.
2. What number comes next? 2, 6, 12, 20, 30, ?
- A. 36
- B. 40
- C. 42
- D. 44
Answer: 42
The gaps grow by 2 each time (4, 6, 8, 10, 12), so 30 + 12 = 42. Each term is also n × (n + 1): 6 × 7 = 42.
3. If 5 machines take 5 minutes to make 5 toys, how long would 100 machines take to make 100 toys?
- A. 100 minutes
- B. 20 minutes
- C. 5 minutes
- D. 1 minute
Answer: 5 minutes
Each machine makes one toy in 5 minutes, so 100 machines working together make 100 toys in the same 5 minutes.
4. A patch of water lilies doubles in size every day. It takes 48 days to cover the whole pond. How many days does it take to cover half the pond?
- A. 24 days
- B. 36 days
- C. 46 days
- D. 47 days
Answer: 47 days
Because the patch doubles daily, it covers half the pond just one day before it covers all of it — on day 47.
- Advertisement
5. How many months of the year have at least 28 days?
- A. 1
- B. 2
- C. 6
- D. 12
Answer: 12
Every month has at least 28 days — February is simply the only month that sometimes has exactly 28.
6. A farmer has 17 sheep. All but 9 run away. How many sheep does the farmer have left?
- A. 9
- B. 8
- C. 0
- D. 17
Answer: 9
'All but 9' means every sheep except 9 ran away, so 9 remain. The trap is subtracting 9 from 17.
7. What number comes next? 1, 1, 2, 3, 5, 8, ?
- A. 11
- B. 13
- C. 14
- D. 16
Answer: 13
Each number is the sum of the two before it (5 + 8 = 13). Indian scholars such as Virahanka described this sequence centuries before Fibonacci made it famous in Europe.
8. On a standard clock, what is the angle between the hour and minute hands at exactly 3:15?
- A. 7.5°
- B. 0°
- C. 15°
- D. 22.5°
Answer: 7.5°
At 3:15 the minute hand points at the 3, but the hour hand has moved a quarter of the way towards the 4 — a quarter of 30°, which is 7.5°.
9. 10 people are at a party, and every person shakes hands exactly once with every other person. How many handshakes take place in total?
- A. 90
- B. 100
- C. 45
- D. 50
Answer: 45
Each person shakes 9 hands, giving 10 × 9 = 90, but that counts every handshake twice, so the answer is 90 ÷ 2 = 45.
10. A father is 4 times as old as his son. In 20 years, he will be exactly twice as old as his son. How old is the son now?
- A. 5 years
- B. 10 years
- C. 15 years
- D. 20 years
Answer: 10 years
If the son is 10, the father is 40; in 20 years they will be 30 and 60, and 60 is exactly twice 30.