AMC8 1990

AMC8 1990 · Q14

AMC8 1990 · Q14. It mainly tests Ratios & proportions, Probability (basic).

A bag contains only blue balls and green balls. There are 6 blue balls. If the probability of drawing a blue ball at random from this bag is $\frac{1}{4}$, then the number of green balls in the bag is

一个袋子里只有蓝球和绿球。有6个蓝球。从袋中随机抽取一个蓝球的概率是$\frac{1}{4}$，则袋子里的绿球数是

(A) 12 12

(B) 18 18

(D) 30 30

(E) 36 36

Answer

Correct choice: (B)

正确答案：（B）

Solution

Blue $\frac{1}{4}$, 6 blue, total 24 balls, green 18. Or green 3 times blue: $3\times6=18$.

蓝球占$\frac{1}{4}$，6个蓝球，总数24个球，绿球18个。或者绿球是蓝球的3倍：$3\times6=18$。

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