17 Math Riddles for Adults With Answers

17 Math Riddles for Adults With Answers


1.How many times does the long hand of the clock pass the short hand between midnight one day and midnight the following day? As both hands are together at the starting time of midnight this does not count as a pass.

Answer

21


2.How can you make the following equation true by drawing only one straight line: 5+5+5=550 Can you figure it out?

Answer

There are two ways to do so:

Draw a line on the first plus sign to turn it into a 4.

Change the equal symbol to a crossed-out equal symbol which means “not equal to.”


3.What number do you get when you multiply all of the numbers on a telephone’s number pad?

Answer

Zero, because any number multiplied by 0 will always equal 0.


4.You go to the doctor because you are ill, and he prescribes you with three pills and tells you to take them every half hour. How long do the pills last you?

Answer

An hour because the first pill doesn’t take 30 minutes to take.


5.Where can you add 2 to 11 and get 1?

Answer

On a clock


6.Once I’m 24. Twice I’m 20. Three times I’m inappropriate. What am I?

Answer

The letter “X”


7.In a lake, there is a patch of lily pads. Every day, the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long would it take for the patch to cover half the lake?

Answer

The patch doubles in size every day and so on the 47th day the patch will be half the size it is on the 48th day.


8.An apple is 40 cents, a banana is 60 cents. and a grapefruit is 80 cents. How much is a pear?

Answer

Forty cents, because the price of each fruit is calculated by multiplying the number of vowels by 20 cents.

9.Anna wrote all the numbers from 300 to 400 on a piece of paper. How many times did she write the digit 3?

Answer

She wrote it 120 times.


10.How many bricks does it take to complete a building made of brick?

Answer

Only one – the “last” one


11.How many days are there in 4 years?

Answer

The answer is 1461, because (365 x 4) + 1. One of the years is a leap year.


12.A bat and a ball cost $1.10. The bat costs one dollar more than the ball. How much does the ball cost?

Answer

The ball costs 5 cents, not 10 cents. If one dollar more than 10 cents is $1.10, then $1.10 + 10 cents is $1.20. Therefore, the ball costs 5 cents.


13.Harry is 54 years old, and his mother, Anna, is 80. How many years ago was Anna three times the age of her son Harry?

Answer

41 years ago


14.You have accidently left out the plug and are attempting to fill the bath with both taps full on. The hot tap takes 6 minutes to fill the bath. The cold tap takes 2 minutes and the water empties through the plug hole in 4 minutes. In how many minutes will the bath be filled?

Answer

2 minutes and 24 seconds


15.The day before yesterday I was 21, and the next year, I will be 24. What day is my birthday?

Answer

31st December, because it must be on the 1st of January, when I turned 22 and so 21 the day before. As it is now a new year, I will be 23 this year and so 24 next year.


16.If it were two hours later, it would be half as long until midnight as it would be if it were an hour later. What time is it now?

Answer

9 p.m.


17.A man is walking down a street night at a constant pace. As he passes the street light, he notices that his shadow becomes longer. Does the top of his shadow move faster, slower, or the same when the shadow is longer than when it is shorter?

Answer

This point maintains a constant speed, independent of the length of the shadow.

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