7/8 + x = 1
subtract 7/8 from each side
x = 1-7/8
x = 8/8 - 7/8
x = 1/8
1 in 38.
Nothing much to say about this problem. There are 38 spaces on the roulette wheel and an every space on a fair wheel has an equal probability of being selected. So you would expect 1/38 = 0.026315789 = 2.6315789% of the time for the number 21 to show up.
If Angie and her friends ate 3/4 of a pizza, that means that 1/4 is left.
Joe ate 2/3 of 1/4 of a pizza. To find out how much he ate, multiply 1/4 by 2/3.

because you multiply fractions straight across.
Your answer is 2/12 or
<em>1/6 of the pizza</em>
You didn't enter a valid question.