Question 59

The average age of a group of 6 sisters decreases by 12 years immediately when a pair of twins is born. What is the total age of all 8 siblings immediately after the birth of the twins?

Solution

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Let the average of all the sisters before the birth of the pair of twins is X.

So, the sum of their ages = 6X

When the pair of twins born, the sum of their ages would remain the same.

Hence, the average of their ages when the pair of twins born = 6X/8 or 3X/4

So, the average decreased by 12 i.e. X - 3X/4 = 12

X/4 = 12

Or, X = 48

Therefore, the sum of their ages when the pair of twins born = 6*48 = 288

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