Question

In 20 spins, about how often can you expect to land on a number evenly divisible by 2? The spinner is 1-8. Theorectical probability.

Answer 1

You can expect to land on a number divisible  by two 50% of the time, 
as their are 4 options of evens to land on, and 4 odds to land on.

Answer 2

There are 4 numbers from 1 - 8 that are divisible by 2... 2,4,6, and 8. So each time you spin you have a 4/8 chance to land on one of them. This reduces to a 1/2 chance. If we spin 20 times, each time we have a 1/2 chance so...

1/2 = x/20
x= 1/2 × 20 = 10

Theoretically you'll spin a number divisible by 2, 10 times in 20 spins.