NTA Abhyas JEE Main2020MathematicsProbabilityPractice

A purse contains 10 ten rupee coins and 5 five rupee coins. Two coins are randomly drawn. If the expected value of 2 drawn coins is λ , then 9 λ 4 is equal to

Correct answer

37.5

Step-by-step solution

2 coins can be both 10 rupee coins, both 5 rupee coins or one 5 rupee coin and one 10 rupee coin So, expected value = 10 C 2 15 C 2 × 20 + 10 C 2 15 C 2 × 10 + 10 C 1 5 C 1 15 C 2 × 15 = 3 7 × 20 + 2 21 × 10 + 10 21 × 15 = 350 21 = 50 3

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