The average of 30 numbers is 55. The average of the

Solution

Sum of all 30 terms = 30 x 55= 1650 Sum of first 15 terms = 15× 51 = 765 Sum of last 12 terms = 12 x 56 = 672 After removing the first 15 and last 12 terms, there will be 3 terms remaining.   Sum of remaining 3 terms = 1650 (765 +672) = 213 According to the question, 68 and 74 are added to the sum of 3 terms. Thus, the number of total terms becomes 5. Average of 5 terms = (213 +68 + 74)/5 = 71   71 is the average of 68, 74 and the remaining 3 numbers.