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Nitin has taken the subjects mathematics, physics and chemistry. The probability of him getting grade A in these subjects are respectively 0.2, 0.3 and 0.9. Getting grades in different subjects are regarded as independent events. The probability of getting A grade by him, either in mathematics or physics, is

Solution

Correct Option: 1

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 0.440.44.

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