Question
The average of 30 numbers is 72. If the average of the
first 12 numbers is 60 and the average of the last 19 numbers is 80, find the 12th number.Solution
ATQ,
Sum of all 30 numbers = 30 × 72 = 2160
Let the 12th number be ‘x’
Sum of first 12 numbers = 12 × 60 = 720
Sum of last 19 numbers = 19 × 80 = 1520
Now, 12th number is included in both groups:
720 + 1520 - x = 2160
=> 2240 - x = 2160
=> x = 2240 - 2160
=> x = 80
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