Answer:
50 people didn't participate in any activity
Explanation:
total people = 500
people who gave blood = 225
people who helped in cleaning = 153
people who gave blood as well as helped in cleaning = 72
total number of people who participated in activities,
= 225 + 153 + 72 = 450
people who didn't participate in any activity = 500 - 450 = 50