In a class there are 16 boys and 9 girls. The teacher wants to select either a boy a girl as a class representative. In how many ways can the teacher make the selection?

Explanation

Here the teacher is to perform either of the following two operations:
(i) selecting 1 boy out of 16 boy,
and (ii) selecting 1 girl out of 9 girls.
The first of these can be performed in 16 ways and the second in 9 ways.
By the fundamental principle of addition, either of the two operations can be performed of addition, either of the two operation can be performed in (16 + 9) ways = 25 ways.
Hence, the teacher can make the selection of 1 boy or 1 girl in 25 ways.