100+ Challenging math riddles to keep your mind sharp

Explanation :  $40 (10 at $4, or 8 at $5)

Explanation :  The nail would be at the same height since trees grow at their tops.

Explanation :  

If you look carefully at the image, you'll see that the dots are placed in intersection of many circles. So, The correct answer is 12.

Explanation :  

Let the duck be ‘Du’

The dog be ‘Do’

The rabbit be ‘R’.

From the above picture,

we can form equations as,

R + Du = 10kg.…equation (1)

R + Do = 20kg….equation (2)

Do + Du = 24kg…equation (3)

& R + Do + Du = ?

Rearranging the equations,

equation (1) = R + Du = 10kg

Du = 10kg – R

equation (2) = R + Do = 20kg

Do = 20kg – R

Putting the values of Do & Du in equation (3),

Do + Du = 24kg

20kg – R + 10kg – R = 24kg

30kg – 2R = 24kg

2R = 6

Rabbit, R = 3kg

Substituting the value of R, in equation (1) & equation (2)

We get,

equation (1), R + Du = 10kg

3 + Du = 10kg

Duck, Du = 7kg

Also, equation(2), R + Do = 20kg

3 + Do = 20kg

Dog, Do = 17kg.

Adding the values of,

Do + Du + R = 3 + 7 + 17

Dog + Duck + Rabbit = 27kg.

Explanation :  

2/1 =2 
2*1 = 2
2-1= 1
so answer is 1

Explanation :  

9-9=0. Move one from the addition sign to make it a subtraction sign, and put it to 3 to make 9, 2. move one from 8 to make it 9.

Explanation :  

horizontal multiplication - vertical multiplication
6*6 - 7*5 = 1
for answer 7*3 - 9*2 = 3

Explanation :  

just put the values of the balls and add them you will get 15

Explanation :  

Count step by step without leaving any triangle formation

Explanation :  

7 large boxes (7 x 8 = 56 boxes)
4 small boxes (4 x 10 = 40 boxes)
So the answer is 11 total cartons for 96 boxes

They are 2, 2, and 9.

Explanation :  

If you list out the trio of factors that multiply to 36, you get: 1 1 36 = 38 1 2 18 = 21 1 3 12 = 16 1 4 9 = 14 6 6 1 = 13 2 2 9 = 13 2 3 6 = 11 3 3 4 = 10 If the sum is 13, as you can see, there are 2 options. When she sa ys her 'oldest' you know it cannot be {6, 6, 1} since she would have two 'older' sons, not an 'oldest'.

Explanation :  

The outer number is the sum of the numbers in the two segments immediately across the line connecting big Circle to small Circle.

i.e.
5+6=11,
6+2=8,
2+8=10,
8+1=9,
1+4=5,
4+7=11,
7+9=16
therefore, 
9+5 =14

Explanation :  

first digit * first digit
third digit * third digit 
398 = 964 (3*3 8*8). So 423 = 169 (4*4 3*3)

She will never get to the 1-foot mark because you keep adding smaller and smaller amounts!

Explanation :  

We will find the maximum value of this process, when this is carried out infinite times.

This process goes like a Infinite GP, whose
First term,a = 1/2ft.
Common Ratio, r = 1/2ft.

Maximum value of this process is One Foot when the athlete jumps forever or Practically, she will never complete her 1 foot.

Hence, Athlete will never complete. her complete .
Here,
As shown in Number line, since we are taking half distance of the previous one.
Starting from 1/2 ft. ,and ending at 1 foot.
The value always tends towardd 1 but never reaches one.

2

Explanation :  

The answer will be 2. Look at how many closed areas there are.
9999 has 4 closed areas (the top of the '9').
8888 has 8 closed areas (the top and bottom parts of 8 and there are no other digits).
1816 has 3 closed areas (top and bottom of 8 and bottom of 6, and it has 2 other digits (3 * 2 = 6)).
1212 has 0 closed areas, (0 * 4 = 0),
Therefore,
1919 has 2 closed areas. (the top of the '9').