Answer:
220
Step-by-step explanation:
Let M represent the amount of people that drank milk, let T represent the people that drank tea.
Let x represent the people that drank both milk and tea.
Therefore. the amount of people that drank only milk = n(M ∩ T') = 620 - x
the amount of people that drank only milk = n(M' ∩ T) = 350 - x
The amount of people that did not drink any of them = n(M ∪ T)'
Since 800 people participated, Hence:
620 - x + (350 - x) + x + 50 = 800
620 + 350 + 50 - x - x + x = 800
1020 - x = 800
x = 1020 - 800
x = 220
Therefore 220 people drank both drinks.