Question

数字和为 $7$ 的两位正整数有多少个？

Find the number of two-digit positive integers whose digits total $7.$

$6$

$7$

$8$

$9$

$10$

十位数字不能是 $0$

The tens digit cannot be $0.$

一旦选定十位数字，个位数字就确定了

Once the tens digit is chosen, the ones digit is forced.

十位数字可以从 $1$ 到 $7$ ，而这个数字会确定个位数字。

因此共有 $7$ 个数。

所以正确答案是 B。

Note that the tens digit can range from $1$ to $7,$ and this digit determines the units digit.

Therefore, there are $7$ numbers.

Thus, B is the correct answer.