Question

Rohan 在四个鱼缸中共养了九十条孔雀鱼。

• 第二个鱼缸比第一个多一条孔雀鱼。

• 第三个鱼缸比第二个多两条孔雀鱼。

• 第四个鱼缸比第三个多三条孔雀鱼。

第四个鱼缸中有多少条孔雀鱼？

Rohan keeps a total of 90 guppies in 4 fish tanks.

• There is 1 more guppy in the 2nd tank than in the 1st tank.

• There are 2 more guppies in the 3rd tank than in the 2nd tank.

• There are 3 more guppies in the 4th tank than in the 3rd tank.

How many guppies are in the 4th tank?

$20$

$21$

$23$

$24$

$26$

答案：E

知识点：一次方程

难度评级：980

视频讲解：

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文字解答：

设第一个鱼缸有 $x$ 条，则四个鱼缸分别有 $x$ 、 $x+1$ 、 $x+3$ 和 $x+6$ 条。由总数可得 $x + x + 1 + x + 3 + x + 6 = 90$ $4x+10=90$ $x=20.$

题目问的是第四个鱼缸的数量，不是第一个鱼缸。因此第四个鱼缸有 $x+6=20+6=26$ 条。

正确答案是 E。

Let $x$ be the number of guppies in the 1st tank. Hence, there are $x+1$ guppies in the 2nd tank, $x+3$ guppies in the 3rd tank, and $x+6$ guppies in the 4th tank. We then use the fact that there are a total of 90 guppies in the 4 tanks to find $x$ : $x + x + 1 + x + 3 + x + 6 = 90$ $4x+10=90$ $x=20.$

Note that we are not yet done since we are asked for the number of guppies in the 4th tank and not the 1st. There are $x+6=20+6=26$ guppies in the 4th tank.

Thus, E is the correct answer.

2024 AMC 8 第 12 题

答案：E

难度评级：980

视频讲解：

文字解答：

其他年份的第 12 题