The probability of Nitin getting grade A in Mathematics or Physics (or both) needs to be found.
Given:
P(A in Math) = 0.2
P(A in Physics) = 0.3
P(A in Chemistry) = 0.9
All events are independent.
For the probability of "A OR B":
P(A or B) = P(A) + P(B) - P(A and B)
The term P(A and B) is subtracted because when adding P(A) + P(B), the case where both happen is counted twice.
Since the events are independent:
P(Math AND Physics) = P(Math) × P(Physics)
P(Math AND Physics) = 0.2 × 0.3
P(Math AND Physics) = 0.06
P(Math OR Physics) = P(Math) + P(Physics) - P(Math AND Physics)
P(Math OR Physics) = 0.2 + 0.3 - 0.06
P(Math OR Physics) = 0.5 - 0.06
P(Math OR Physics) = 0.44
Therefore, the probability of getting A grade in either Mathematics or Physics is 0.44.