It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?

In a science lab, a petri dish hosts a healthy colony of yeast for an experiment. Now every minute, all the yeast cells divide into two. At noon, there was just a single cell of yeast and at 1:22, the Petri dish was half full. Can you calculate when the dish will be full of yeast?

Can you find out which triangle will have a bigger area among the following?
1. A triangle with sides 300, 400 and 500
2. A triangle with sides 300, 400 and 700

Count the number of squares in the picture below.

In which direction should the missing arrow point?

Can you count the number of triangles inside a triangle?

How many minutes are there in Feb 2017?

Note: The shortest answer is the correct answer.

What number when divided in half becomes zero?

We have arranged an array of numbers below. What you have to do is use any kind of mathematical symbol you know excluding any symbol that contains a number like cube root. You can use any amount of symbols but you have to come up with a valid equation for all of them.

0 0 0 = 6
1 1 1 = 6
2 + 2 + 2 = 6
3 3 3 = 6
4 4 4 = 6
5 5 5 = 6
6 6 6 = 6
7 7 7 = 6
8 8 8 = 6
9 9 9 = 6