Probability

$\frac{\mbox{Total number of all possible solutions}}{\mbox{Total number of all solutions}}$

You can choose 100 numbers so 

$\frac{n}{100}$ .

There are 50 numbers that are divisible by 2 in the set { 1, 2, 3, ..., 100 }.

In the set { 1, 2, 3, ..., 100 } there are 12 numbers divisible by 8.

Every multiple of 8 is divisible by 2, so (50 - 12 =) 38 possible solutions. (n = 38)

$\frac{38}{100} = \frac{19}{50} = 0.38 = 38\%$