Explanation:
a)
we have 400 people. that is 10/10 of the whole group.
7/10 of the whole group drink tea. that is
400 × 7/10 = 40 × 7 = 280
that leaves 3/10 of the whole group not drinking tea
400 × 3/10 = 40 × 3 = 120
from the 280 tea drinkers 20% drink at lay e cups of tea each day. that is
280 × 20/100 = 28 × 2 = 56
because 20 out of 100 is the meaning of 20%.
and the remaining 80% of the tea drinkers drink less then 3 cups each day.
280 × 80/100 = 28 × 8 = 224
b)
out of the 400 people 56 drink at least 3 cups of tea each day. that is
56/400 = 7/50