Shortcut Trick
Sum of ages of Ram, Shyam, and Rahim = Sum of all given averages = 28 + 26 + 30 = 84 years.
Ram's age = 84 − (26 × 2) = 84 − 52 = 32 years.
Shyam's age = 84 − (30 × 2) = 84 − 60 = 24 years.
Rahim's age = 84 − (28 × 2) = 84 − 56 = 28 years.
∴ The correct answer is 32 years, 24 years and 28 years.
Alternate Method
Given:
Average age of Ram (R) and Shyam (S) = 28 years
Average age of Rahim (Rh) and Shyam (S) = 26 years
Average age of Ram (R) and Rahim (Rh) = 30 years
Formula Used:
Sum of observations = Average × Total number of observations
⇒ R + S = 28 × 2 = 56 --- (i)
⇒ Rh + S = 26 × 2 = 52 --- (ii)
⇒ R + Rh = 30 × 2 = 60 --- (iii)
Adding equations (i), (ii), and (iii):
⇒ 2(R + S + Rh) = 56 + 52 + 60 = 168
⇒ R + S + Rh = 168 ÷ 2 = 84 --- (iv)
Subtracting (ii) from (iv):
⇒ Ram's age (R) = 84 − 52 = 32 years
Subtracting (iii) from (iv):
⇒ Shyam's age (S) = 84 − 60 = 24 years
Subtracting (i) from (iv):
⇒ Rahim's age (Rh) = 84 − 56 = 28 years
∴ The correct answer is 32 years, 24 years and 28 years.
Additional Information
Definition of Average
Average is the ratio of the sum of values to the number of values. Formula: Average = Sum ÷ n.
Sum of Pairs Property
In a group of three (A, B, C), if sums of pairs (A+B, B+C, C+A) are known, the total sum (A+B+C) is exactly half of the sum of the three pair sums.
Weighted Average
When two groups with averages A1 and A2 and sizes n1 and n2 are combined, the new average is (n1A1 + n2A2) ÷ (n1 + n2).