In this case, we'll have to carry out several steps to find the solution.
Step 01:
Data
Junior
Morning 17
Afternoon 20
Evening 3
Step 02:
Junior
probability afternoon = junior afternoon / total junior afternoon
total junior afternoon = 17 + 20 + 3 = 40
probability afternoon = 20 / (17 + 20 + 3) = 0.5
The answer is:
probability afternoon = 0.5