Do you think mathematical riddles about counting and logic are only for schoolchildren? No matter how! It is also helpful for adults to shake the old days and stretch their brains a little with the help of not very complex, but exciting and not always standard riddles about the score.
Ready to test yourself with 55 questions? If so, scroll down below, and let's get started!
Questions will always be accompanied by an answer, which you will see below. But don't peek!
Mathematical tasks for intelligence (with answers)
1. What number will you get if you multiply all the numbers on the phone's numeric keypad?
Zero because any number multiplied by 0 will always be zero.
2. Where can you add 2 to 11 and get 1?
On the clock.
3. The duck got $9, the spider got $36, and the bee got $27. Based on this information, how much money will the cat be given?
$18 ($4.50 per paw).
4. When Josh was 8 years old, his brother was half his age. Now that Josh is 14, how old is his brother?
His brother is 10 years old. Half of 8 is 4, so Josh's brother is 4 years younger. When Josh is 14, his brother is still 4 years younger, so he is 10.
5. When my father was 31, I was 8. Now he is twice my age. How old am I?
The age difference is 23 years, so the son must be 23 if the father was twice as old.
6. How many sides does a circle have?
Two - inside and outside.
7. What is heavier - a kilogram of iron or a kilogram of down?
Their weight is the same.
8. What is the most common digit between numbers from 1 to 1000 inclusive?
Hint: look for a pattern!
The most common number is 1! Do you understand why? Each number from 1 to 9 occurs exactly the same number of times in every ten numbers. But since the number 1000 was included, the number 1 appears one more time in the number series.
So, in total, the number 1 occurs 301 times, while all other numbers occur in the series 300 times.
9. How many bricks does it take to build a brick building?
Only one is the last one.
10. A bat and a ball cost $1.10. The bat costs one dollar more than the ball. How much is the ball worth?
If the ball really cost 10 cents, then a bat that costs $1 more than it would cost $1 + 10 cents. This contradicts the conditions of the problem. Let's take a look at the solution. Let's say the price of the ball is X. The bat costs $1 more, X + 1. The equation is: X + (X + 1) = 1.1 because the bat and ball together cost $1.1. We solve the equation:
2X + 1 = 1.1;
2X = 1.1 - 1;
X = 0.05.
So the ball costs 5 cents and the bat costs $1.05.
11. Can you arrange four nines to make 100?
99+9/9 = 100.
12. When John was six years old, he drove a nail into his favorite tree to mark his height. Ten years later, at the age of sixteen, John returned to see how much taller the nail was. If a tree grew five centimeters every year, how much taller would a nail be?
The nail will be at the same height as the trees grow from the top.
13. When Mitch was 6 years old, his younger sister Lila was six months old. If Mitch is 40 today, how old is Lila?
She is 37 years old.
14. You are given 3 positive numbers. You can add these numbers and multiply them together. The result you get will be the same in both cases. What numbers?
1, 2 and 3
Both addition and multiplication give the same result.
15. The day before yesterday I was 21, and next year I will be 24. What day is my birthday?
If today is January 1st, then your birthday is December 31st. The day before yesterday (December 30) you were still 21 years old, yesterday (December 31) you turned 22 years old, this year you will be 23 years old, and next year - 24 years old.
16. Add me to you and multiply by 4. Divide me by 8 and you will have me again. What number am I?
17. How did a football fan know before a game that the score would be 0-0?
Before the game the score is always 0:0.
18. If you multiply this number by any other number, the answer will always be the same. What is this number?
19. What is the next number in the row? 7645, 5764, 4576, …
6457 because the last digit is moved forward to get the next number in the series.
20. What can be put between 7 and 8 so that the result is more than seven, but less than eight?
It's 7.8. It is greater than 7 but less than 8.
21. If two is a company and three is a crowd, what are four and five?
22. More than an hour, less than a minute
23. Old Granny Adams left half of her money to her granddaughter and half of that amount to her grandson. She left a sixth to her brother and the remainder, $1,000, to a dog shelter. How much did she leave?
The trick is to focus not on hypothetical amounts but on fractions: Adding half, a quarter and one sixth tells us that the sum is a fraction of twelve (2+4+6=12). You can also think of this as 6/12, 3/12, 2/12, which equals 11/12. If the balance is $1,000, it should be one twelfth, so the total is $12,000.
24. You know that 2 + 2 equals 2x2. Now find a set of three distinct integers whose sum is equal to their sum when multiplied
The three distinct integers whose sum when multiplied equals their sum are 1, 2 and 3.
25. What number will decrease by 12 units if you write it down and turn the sheet upside down?
Answer 86. If you turn the sheet with this number over, you get 98, which is 12 more than 86.
26. If it were now two hours later, then there would be half as much time left until midnight as if it were now an hour later. What time is it now?
21:00. 9 pm.
27. A woman walks down the street at night at a constant pace. As she passes a street lamp, she notices that her shadow is getting longer. Does the top of her shadow move faster, slower, or the same way when the shadow is longer than when it's shorter?
This point maintains a constant speed, independent of the length of the shadow.
28. The builder has 8 bricks. Seven of them weigh the same, and one is slightly heavier. How can he, using the scales, find a heavier brick in two weighings?
Let's divide the bricks into 2 groups: the first group - 6 bricks, the second group - 2 bricks. On each scale we put 3 bricks from the first group. There are two options after weighing:
Outweigh one of the scales.
The scales will keep the balance.
In the first case, we put one brick from a heavier group on each scale. If the scales maintain balance, then the defective brick is the third brick from this group, if one of the bowls outweighs, the defective brick is on this bowl.
In the second case, we put one brick from the second group on each scale. Outweigh the bowl on which the defective brick is located.
29. Two boys played checkers for 2 hours. How long did each boy play?
30. A man dies of old age on his 25th birthday. How is this possible?
He was born on February 29th.
31. If you are 80 centimeters from the door and with each step you move half the distance to the door, how many moves will it take to get to the door?
You will never reach the door, because it will always be half the distance, no matter how small it is.
32. If one bee sits on each flower, then one bee will remain without a flower, and if 2 bees sit on each flower, then one flower will remain without a bee. How many flowers and bees?
4 bees and 3 flowers.
33. If you go to the cinema and take your friends with you, is it cheaper to take one friend to the cinema twice or two friends to the cinema at the same time?
It's cheaper to take two friends at the same time.
34. Which month has 28 days?
35. What number increases and does not decrease?
36. You have 4 apples, you remove 3, how many do you have left?
37. If you buy a rooster and expect to get three eggs every day for breakfast, how many eggs will you have in three weeks?
Not at all, because roosters don't lay eggs.
38. The miller went to the mill and saw 3 cats in each corner. How many legs are on the mill?
39. 6 people built a barn in 9 hours. How long will it take 12 builders to build the same barn?
No way, because it's already built.
40. A farmer has 17 sheep and all but 9 die. How much is left?
41. A train 300 meters long is moving at a speed of 300 meters per minute and must pass through a tunnel 300 meters long. How long will it take the train to pass the tunnel?
Two minutes because the front of the train takes one minute and the rest of the train takes two minutes to go through the entire tunnel.
42. I add five to nine and get two. The answer is correct, but how?
When it is 9 pm, add 5 hours to that and you get 2 pm.
43. In a strange little town there was a strange little stream with strange little fish in a strange little flock. A stranger approached a local fisherman and asked how much his strange fish weighed. The strange man replied: “All the fish in this stream weigh exactly ½ kilogram plus ½ of the fish. Isn't that weird? How many kilograms does the strange little fish weigh?
44. You put three matches on the table and then asked a friend to add two more matches to make eight. How can he do it?
From two matches, make the Roman numeral five and add it to three to get the Roman numeral eight.
45. A girl has as many brothers as sisters, only each brother has half as many brothers as sisters. How many brothers and sisters does this family have?
Four sisters and three brothers.
46. A man is twice as old as his younger sister. He is also half their father's age. In 50 years, the age of the sister will be half the age of their dad. How old is the man now?
He's 50 years old.
47. If seven people meet each other and each shakes hands with each other only once, how many handshakes will there be?
48. Three doctors said that Bill was their brother. But Bill claims he has no brothers. How many brothers does Bill actually have?
No one. He has three sisters who are doctors by profession.
49. How can you make the following equation correct by drawing only one straight line: 5+5+5 =550. Can you figure it out?
There are two ways to do this:
Draw a line on the first plus sign to turn it into a 4.
Replace the equals symbol with a crossed out equals symbol, which means "not equal".
50. There are 8 benches in the park. Three have been painted.
How many benches are there in the park?
51. Apple - 60 kopecks, banana - 60 kopecks, grapefruit - 60 kopecks. How much is a pear?
120 kopecks, because the price of each fruit is calculated by multiplying the number of vowels by 20.
52. Anna wrote all the numbers from 300 to 400 on a piece of paper. How many times did she write the number 3?
53. How many times during the day do the minute and hour hands of a clock form a right angle?
In 1 hour, the hour hand describes an angle of 30 °, and in 1 minute. − angle 0.5°. Minute hand for 1 min. describes an angle of 6°. Since 90 : (6 − 0.5) = 16 (4/11), the minute and hour hands form a right angle for the first time after 16 (4/11) minutes. after both are at 12. Since n × 16 (4/11) = 24 × 60, we get n = 88 (this number includes the angles of 0°, 90°, 180° and 270° formed minute and hour hands).
54. Arrange brackets and mathematical signs so that the equality is true: 9999999 = 100
(99-9):9 + (99-9) = 100;
(99-99)* 999 = 10*0 and a number of other ways.
55. What will always be in front of you and yet you will never see it?