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
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 0.44
Let \(E_1\) and \(E_2\) be the events of grade A in mathematics and in physics:
\(P(E_1) = 0.2,\quad P(E_2) = 0.3\)
Grade A in mathematics or physics means at least one of the two, the event \(E_1 \cup E_2\). Since the events are independent,
\(P(E_1 \cap E_2) = 0.2 \times 0.3 = 0.06\)
By the addition rule:
\(P(E_1 \cup E_2) = 0.2 + 0.3 - 0.06 = 0.44\)
The chemistry probability 0.9 is not needed.