Question

可以用多少种不同的 $\$5$ 纸币和 $\$2$ 纸币组合凑成总额 $\$17$ ？本题中顺序不重要。

How many different combinations of $\$5$ bills and $\$2$ bills can be used to make a total of $\$17?$ Order does not matter in this problem.

$2$

$3$

$4$

$5$

$6$

因为 $\$17$ 是奇数， $\$5$ 纸币的张数必须是奇数。

Because $\$17$ is odd, the number of $\$5$ bills must be odd.

尝试不会超过总额 $\$17$ 的奇数张 $\$5$ 纸币。

Try the possible odd numbers of $\$5$ bills before the total goes over $\$17.$

因为总额 $\$17$ 是奇数， $\$5$ 纸币的张数必须是奇数。

一张 $\$5$ 纸币还剩 $\$12$ ，也就是六张 $\$2$ 纸币。三张 $\$5$ 纸币还剩 $\$2$ ，也就是一张 $\$2$ 纸币。五张 $\$5$ 纸币太多。

因此共有 $2$ 种组合。

所以正确答案是 A。

Since the total $\$17$ is odd, the number of $\$5$ bills must be odd.

One $\$5$ bill leaves $\$12,$ which is six $\$2$ bills. Three $\$5$ bills leave $\$2,$ which is one $\$2$ bill. Five $\$5$ bills is too much.

Therefore, there are $2$ combinations.

Thus, A is the correct answer.