Question
There are 15 numbers such that average of first 12
numbers is 20 while the average of last five numbers is 40. Find the 12th number, if the ratio between 11th and 12th number is 9:7, respectively.Solution
Sum of first 12 numbers = (12 x 20) = 240 Sum of last 5 numbers = (40 x 5) = 200 Sum of 11th and 12th number = (240 - 200) = 40 So, 12th number = 40 x (7/16) = 17.5
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