Mind Refreshing Puzzle - A boy goes to his grand parents house.

A boy goes to his grand parents house. There he either does   yoga in the morning / plays tennis in the evening / does neither. 

However he does not do both on the same day. 

We know that 22 days he did either 1 activity. 

24 mornings he did nothing. 

12 evenings he did nothing. 

How many min days did he stay there to have done this? 

Answer

We get three equations: 

1. Yoga + Tennis =22 

2. Tennis + Nothing=24 

3. Yoga + Nothing = 12 

We are able to conclude: Yoga = 5, Tennis = 17, Nothing =7. 

Hence the min days: 5+17+7=29 days