Of the 50 guests at a party, 10 percent are smokers. How many non-smokers must leave in order to bring the number of smokers up to 50 percent of the guests?

A. 5

B. 10

C. 20

D. 35

E. 40

Kaplan's explanation:

Given 50 guests at a party, of whom 10% are smokers, how many nonsmokers would need to leave in order to have an equal number of smokers and nonsmokers?

Straight math is the best approach to this problem. If 10% of the 50 people are smokers, then there are 10% × 50 = 5 smokers and 50 – 5 = 45 nonsmokers. Smokers will represent 50% — or one-half — of the party guests when there are equal numbers of smokers and nonsmokers; that is, when there are 5 nonsmokers remaining. This means that 40 of the 45 nonsmokers must leave. Answer Choice (E) is correct.

Can someone please explain in a better way the logic to the answer of this problem? I got down:

50 guests @ party:

.10 ---> 5 are smokers

.90 ---> 45 are non smokers

I don't understand why 40 have to leave? It's probably easy but I don't see it.

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