Answer:
Let's denote:
The probability that today is Monday: P(A)
The probability that a student is absent: P(B)
The probability that a student is absent given that day is Monday: P(B|A)
As given,
P(A intersect B) = 3/100
P(A) = 1/5
=> P(B|A) x P(A) = P(A intersect B)
=> P(B|A) = P(A intersect B)/P(A) = (3/100)/(1/5) = 15/100 = 3/20
Hope this helps!
:)