math
posted by sheila on .
if each guest eats 2/3 of a small pizza, how may guests would eat 12 small pizzas.

12/(2/3) = 12 * 3/2 = 18
It takes 3 guests to eat 2 pizzas
So, since 12 = 6*2, it takes 6*3 = 18 guests 
Why did you reverse fraction to multiply?

that is the way you divide by fractions.
you know that 2/4 is the same as 1/2, since there are two 4ths in a half.
(1/2) / (1/4) = 1/2 * 4/1 = 4/2 = 2
dividing by a number is the same as multiplying by its reciprocal, just as subtracting a number is the same as adding its negative.
multiplication and division are inverse operations, as are addition and subtraction.
dividing by 10 is the same as multiplying by 1/10.
dividing by 1/3 is the same as multiplying by 3, since each "one" has three "1/3"s in it, so there are three times as many thirds as there are wholes.