Question
The average age of A and B is 21 years. If A is to be
replaced by C, the average would be 20 years. The average age of C and A is 22 years. Find the age of A.Solution
A + B = 2 × 21 = 42 yr B + C = 2 × 20 = 40 yr C + A = 2 × 22 = 44 yr On adding all three, 2 (A + B + C) = 42 + 40 + 44 = 126 ⇒ A + B + C = 63 ∴ A = (A + B + C) – (B + C) = 63 – 40 = 23 yr
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I. Helium – monoatomic
II. Oxygen – triatomic
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