The average of 21 numbers is 12. The average of the first 11 numbers is 9 and the average of the last 11 numbers is 15. What is the value of the middle number?
Average of 21 numbers = 12
=> Sum of 21 numbers = $$21 \times 12=252$$
Similarly, sum of first 11 numbers = $$11 \times 9=99$$
Sum of last 11 numbers = $$11 \times 15=165$$
$$\therefore$$ Value of the middle number = $$(99+165) - 252 = 264-252=12$$
=> Ans - (C)
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