Math riddles

A snail is at the bottom of a 20 meters deep pit. Every day the snail climbs 5 meters upwards, but at night, it slides 4 meters back downwards.
How many days does it take before the snail reaches the top of the pit?

Answer

The snail reaches the top of the pit on the 16th day!

Two trains 200 km from each other are moving at the speed of 50 km/hour to encounter. From one train a fly takes off, flying straight (upon the rails) to the other train at the speed of 75 km/hour, bounces away from it and flies back to the first train. This is repeated till the trains crash to each
other and the fly is smashed.
What distance is the fly able to fly until its judgement moment?

Answer

There is a complicated way counting a sequence. Or simply knowing that if the fly is
flying the 2 hours still at the same speed of 75 km/h then it flies a distance of 150 km.

If I have to take a pill every 1/2 hour,
¿how many do I take in 1 1/2 hours?

Answer

4 pills (one now and every 1/2 hour after that)

Jane is thinking of two whole numbers, and asks Freddy to work out what they are.
The only clue she will give him is that their product is three times larger than their sum.
Can you work out what the two numbers are?

Answer

4, 12

A walk at 4 km/hr. Three hours after A started, B cycles at 20 km/hr towards A.
How far from the start does B catch up with A?

Answer

Let x be the distance in which B catches up with A.

Now time taken by A will be 3 hours more than B.

x/4 = x/20 + 3
x/4 - x/20 = 3
4x/20 = 3
x/5 = 3
x = 15 km

If "M" means "-", "N" means "/", "O" means "+", and "P" means "*"; then find the value of the following:

21 N 7 O 9 P 10 M 13

Answer

80
(21 / 7) + (9 * 10) - 13 = 3 + 90 - 13 = 80

Add me to myself, multiply me by 4, divide me by 8, and you'll have me once more.
What am I?

Answer

Any number.

A Tablet costs $ 100, but for transportation costs, successive increases of 40% and then 20% are made.
What will be your new price?

Answer

Final price with Increase is 140 + 28 = $ 168.

A school bus travels from New Work to Boston. There are four children in the bus. Each child has four backpacks with him. There are four dogs sitting in each backpack. Every dog has four puppies with her. All these dogs have four legs, with four toes at each leg.
What is the total number of toes in the bus?

Answer

The total number of toes is 5170.