Question

some friends participated in a pull - up contest. doing pull - ups how many participants did at least 1 pull - up? participants

Explanation:

Step1: Count participants for each number of pull - ups (excluding 0)

For 1 pull - up: 2 participants.
For 2 pull - ups: 9 participants.
For 4 pull - ups: 3 participants.
For 5 pull - ups: 6 participants.

Step2: Sum up the counts

$$2 + 9+3 + 6$$
$$=11 + 3+6$$
$$=14 + 6$$
$$=20$$

Answer:

20