100+ Challenging math riddles to keep your mind sharp

Explanation :  

The number that should replace the question mark is 9. 
Why? 
The sum of the three numbers on each die equals the number written below it. 
For the first die, for example: 8 + 4 + 7 = 19; 
for the second: 8 + 2 + 1 = 11. 
Following this pattern would explain why the third die is also 11 (5 + 5 + 1) 
and why the mysterious question mark should be 9 (4 + 3 + 2).

Explanation :  

1, 8x8 square
4, 7x7 squares
9, 6x6 squares
16, 5x5 squares
25, 4x4 squares
36, 3x3 squares
49, 2x2 squares
64, 1x1 squares
Therefore, there are actually 64 + 49 + 36 + 25 + 16 + 9 + 4 + 1 squares on a chessboard! (in total 204).

Explanation :  

There will be 24 hours between 9 am today and 9 pm tomorrow.

Assumption- All the activities are performed consecutively without break

Hours consumed = 2+1+1 = 4 hours

Therefore hours remaining = 24 — 4 = 20 hours before 9 am tomorrow

Explanation :  

9 pm, or 21.00 if you prefer military time.

If it were two hours later, it would be 11 pm (23.00) — and one hour to midnight.

If it were one hour later, it would be 10 pm (22.00) — and two hours to midnight.

So, if it were two hours later than it currently is, it would take half as much time to reach midnight as it would if it were one hour later. It’s 9 pm.

Explanation :  

All but nine. that means only 9 is in good condition.

Explanation :  

Assuming there’s a mathematical order to this (not a troll question) the things that stand out would be that all the numbers are divisible by 3 and 9, and the main difference between ducks, spiders, bees, and cats would be the number of legs.

From there we have the following

Duck (2 legs): 3 * 3 = 9 * 1

Bee (6 legs): 3 * 9 = 9 * 3

Spider (8 legs): 3 * 12 = 9 * 4

It’s now easy to see. Therefore, if n = pairs of legs, then the amount of money each animals receives is 9n. A cat with 2 pairs of legs would receive 2 * 9 = $18

Explanation :  

A 30 meters. The time taken by the train to pass the stationary object is equal to the length of the train divided by the speed of the train.

Explanation :  

15 (16+9 ; 6+4)

Explanation :  

B 445 
2=(1+1)1
6=(2+1)2
21=(6+1)3
88=(21+1)4
So 445=(88+1)5

A+8=14
A= 6
9+B = 19
B = 6
D = 19+14 =33
15+ C = D
C = 33-15 = 18

Explanation :  

A = 6. B = 10. C = 18. D = 33

Explanation :  

You see, sometimes it's necessary to compare apples and bananas. Or, in this case,
it could be pears instead of bananas. 
Pear = 9, apple = 6, plum = 4 and these make the answers 7 and 1 respectively.
so 4+9+6 =19.ers 7 and 1 respectively.

Explanation :

Count the cubes carefully. there are cubes underneath other cubes.

Explanation :  

You can see that the red slice of the watermelon is 2, the yellow slice is 3 and the blue one is 1. So, the answer is?5!

Explanation :  

Count the triangle carefully without leaving any triangle inside

Explanation :  

there are four intersecting points.