Question 72
The average of a series of 21 numbers is equal to 43. The average of the first eleven of them is 33. The average of the last eleven numbers is 53. The eleventh number of the series is:
Solution
Average of 21 numbers = 43
Sum of 21 numbers = $$21\times43=903$$
Average of 1st 11 numbers = 33
Sum of 1st 11 numbers = $$11\times33=363$$
Average of last 11 numbers = 53
Sum of last 11 numbers = $$11\times53=583$$
11th number is common in both,
So, 11th number = (583 + 363) - 903 = 43
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