2007 AMC 12B 第 8 题

Question

Tom 的年龄为

T

岁，也等于他三个孩子年龄之和。

N

年前他的年龄是当时三个孩子年龄之和的两倍。求

\frac{T}{N}

。

Tom’s age is

T

years, which is also the sum of the ages of his three children. His age

N

years ago was twice the sum of their ages then. What is

\frac{T}{N}?

2

3

4

5

6

N

年前 Tom 是

T-N

岁；每个孩子也都少

N

岁。

N

years ago Tom was

T-N;

each child was

N

years younger

当时孩子总年龄为

T-3N

；列方程

T-N=2(T-3N)

。

The children then totaled

T-3N;

set

T-N=2(T-3N)

N

年前 Tom 年龄为

T-N

。三个孩子每人少

N

岁，所以他们当时总年龄为

T-3N

。

条件给出

T-N=2(T-3N)\text{，}

因而

5N=T

，所以

\frac{T}{N}=5

。

所以正确答案是 D。

Tom’s age

N

years ago was

T-N.

His three children were each

N

years younger, so their ages then totaled

T-3N.

The condition gives

T-N=2(T-3N),

so

5N=T

and

\frac{T}{N}=5.

Thus, the correct answer is D.

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