2008 AMC 10A 第 12 题

Question

在一堆红、蓝、绿三色弹珠中，红弹珠比蓝弹珠多

25\%

，绿弹珠比红弹珠多

60\%

。设红弹珠有

r

个。这堆弹珠总数是多少？

In a collection of red, blue, and green marbles, there are

25\%

more red marbles than blue marbles, and there are

60\%

more green marbles than red marbles. Suppose that there are

r

red marbles. What is the total number of marbles in the collection?

2.85r

3r

3.4r

3.85r

4.25r

用

r

表示蓝弹珠和绿弹珠数量。

Write the blue and green counts in terms of

r

由

r = 1.25b

得

b = 0.8r

，且

g = 1.6r

。

From

r = 1.25b

we get

b = 0.8r,

and

g = 1.6r

因为

r = 1.25b

，蓝弹珠数为

b = \dfrac{r}{1.25} = 0.8r

。

绿弹珠数为

g = 1.6r

。

总数为

r + 0.8r + 1.6r = 3.4r

。

所以正确答案是 C。

Since

r = 1.25b,

the number of blue marbles is

b = \dfrac{r}{1.25} = 0.8r.

The number of green marbles is

g = 1.6r.

The total is

r + 0.8r + 1.6r = 3.4r.

Thus, the correct answer is C.

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