Question

You have a stack of pennies without counting the pennies, how can you know if there is a odd or even number of them

Answer 1

You can put the pennies in 2 rows, if they match then they are even, if not they are odd

Answer 2

Suppose that you have a stack of pennies. If you want to know without counting whether there is an odd or even number of pennies, then you have to split them into two parts, for example,  placing one coin left and one coin  right.

If the number of pennies is even, then no coins will left, if the number is odd, then one coin will be extra.