Question

一群骑自行车和三轮车的孩子经过 Billy Bob 家。Billy Bob 数到 $7$ 个孩子和 $19$ 个轮子。有多少辆三轮车？

A group of children riding on bicycles and tricycles rode past Billy Bob's house. Billy Bob counted $7$ children and $19$ wheels. How many tricycles were there?

$2$

$4$

$5$

$6$

$7$

答案：C

知识点：方程组

难度评级：720

解答：

设 $b$ 为自行车数量， $t$ 为三轮车数量。可列方程组将第一个方程乘以 $2$ ，再从第二个方程中相减，得到 $t = 5$ 。 $\begin{gather*} b + t = 7, \\ 2b + 3t = 19. \end{gather*}$

所以正确答案是 C。

Let $b$ be the number of bicycles and $t$ be the number of tricycles. Then we can set up the following system of equations: $\begin{gather*} b + t = 7, \\ 2b + 3t = 19. \end{gather*}$ Multiplying the first equation by $2$ and subtracting from the second equation, we get $t = 5.$

Thus, C is the correct answer.

2003 AMC 8 第 4 题

答案：C

难度评级：720

解答：

其他年份的第 4 题