AMC 8 1991 Problem 12

AMC8 1991 年第 12 题

比与比例★★★☆☆

If

\displaystyle \frac{2+3+4}{3}=\frac{1990+1991+1992}{N}

, then N=

若

\displaystyle \frac{2+3+4}{3}=\frac{1990+1991+1992}{N}

，则 N=

A.3
B.6
C.1990
D.1991
E.1992

正确答案 · Correct Answer

D

解析 · Solution

Solution 1

Note that for all integers

n\neq 0

,

\displaystyle \frac{(n-1)+n+(n+1)}{n} =3.

Thus, we must have

N=1991 \rightarrow \text{D}

.

继续练习

免费刷 1991 整卷 →