Math riddles

There are 7 pairs of shoes. Someone takes one of the shoes. How many shoes are left?

Answer

13
because 7+7=14 and 14-1=13

The ages of a father and son add up to 66. The father's age is the son's age reversed.
How old could they be?
(3 possible solutions).

Answer

51 and 15. 42 and 24. 60 and 06.

(4+1)x2+6÷2 =

a) 13
b) 20
c) 25

Answer

a) 13.

A numbered cube has 6 sides. The sides have the numbers 1,2,4,5, 6, and 7. If the cube is thrown once, what is the probability of rolling an even number?

Answer

3/6 = 1/2 = 0.5

# Sides with even number / # Total sides

A cake is split into two pieces. The larger piece from the initial cut is then split into four equal pieces. Let’s say the smaller piece from the first cut combined with two of the tiny pieces from the second cut forms 70% of the cake. Finally, the smaller piece from the first cut is split into two equal halves. How much of the cake is one of those halves?

Answer

20%.
After the first cut, the cake is split into a 40% piece and a 60% piece. The 60% piece is then cut into four 15% pieces, so 40% + 15% + 15% makes 70% of the cake. Then, the 40% piece from the first cut is split into two 20% pieces.

There are two numbers that, when multiplied, give 10000, but neither of them contains a zero.
Which numbers are these?

Answer

16 and 625.

Factorize the number 10000: 10000 = 2 × 2 × 2 × 2 × 5 × 5 × 5 × 5. Neither of the two numbers can contain the combination 2 × 5, because then the last digit of the number is definitely a zero. So one number has to be 2 × 2 × 2 × 2 = 16 and the other number 5 × 5 × 5 × 5 = 625.

You have 20 pairs of black socks and 20 pairs of white socks all mixed up in your sock drawer. There are no lights on so you can't see the color of your socks. What is the smallest number of socks you can pull out of your drawer to make sure you get 1 matched pair of either black or white socks.

Answer

3 because since there are only two sock colors, if you take out three socks two out of three of them have to be the same color

98 % 49 x 12 + 16 -36 = ?

Answer

4

How can you arrange three 5's so they equal 6?

Answer

5/5+5=6 (5/5=1,1+5=6.)

Charles walks over a railway-bridge. At the moment that he is just ten meters away from the middle of the bridge, he hears a train coming from behind. At that moment, the train, which travels at a speed of 90 km/h, is exactly as far away from the bridge as the bridge measures in length. Without hesitation, Charles rushes straight towards the train to get off the bridge. In this way, he misses the train by just four meters! If Charles had rushed exactly as fast in the other direction, the train would have hit him eight meters before the end of the bridge.
What is the length of the railway-bridge?

Answer

The railway-bridge has a length of 44 meters.

Let the length of the bridge be x meters.

Running towards the train, Charles covers 0.5x-10 meters in the time that the train travels x-4 meters. Running away from the train, Charles covers 0.5x+2 meters in the time that the train travels 2x-8 meters.

Because their speeds are constant, the following holds:

(0.5x-10) / (x-4) = (0.5x+2) / (2x-8)
which can be rewritten to

0.5x^2 - 24x + 88 = 0
Using the quadratic formula we find that x=44, so the railway-bridge has a length of 44 meters.

I am a three digit number.
My tens digit is five more than my ones digit.
My hundreds digit is eight less than my tens digit.
What number am I?

Answer

Number 194.

If 3(q-2)=2(q+1)-3,

find the value of q.

Answer

q = 5

3q - 6 = 2q - 1 => q = 5