Out of the four numbers the average of the first three is 16 and that of the last three is 15 If the...........

Quantitative Aptitude ( CCS) Average

Out of the four numbers the average of the first three is 16 and that of the last three is 15. If the last number is 20 then find the average of first number?

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Explanation:

Average of a, b, c first three = 16

total of a + b + c = 16 ×× 3 = 48 ......(i)
Average of last 3 numbers b, c and d = 15
then total (b + c + d) = 15 ×× 3= 45 ......(ii)
from (i) - (ii)
=a + b + c - (b + c + d) = 48 - 45
= a - d = 3 = a - 20 = 3 [d = 20] = a = 23
=Therefore, first number a = 23