SOLUTION: in a set of 12 numbers, if the average of first 5 numbers is 6 and average of all 12 numbers is 7.5, then what is the average of last 7 numbers ?

Question 843041: in a set of 12 numbers, if the average of first 5 numbers is 6 and average of all 12 numbers is 7.5, then what is the average of last 7 numbers ?
Found 2 solutions by Theo, hamsanash1981@gmail.com:
Answer by Theo(13342) (Show Source): You can put this solution on YOUR website!
The average of all the numbers is their total divided by their number.

For the first 5 numbers, their average is equal to 6, so their total is equal to 5 * 6 = 30

For all twelve numbers, their average is equal to 7.5, so their total is equal to 12 * 7.5 = 90

If you subtract the total of the first 5 from the total of all 12, you will get the total of the last 7.

That total is equal to 60.

Divide that total by 7 and you get the average of the last 7.

That average is equal to 8.571428571

If you know the total and you know the number of items that were used to get that total, you can calculate the average by dividing the total by the number.

If you know the average and you know the number of items that were used to get that average, you can calculate the total by multiplying the average by the number.

In algebraic terms:
A = average
T = total value
N = number of data items.

A = T/N
T = A*N

Answer by hamsanash1981@gmail.com(151) (Show Source): You can put this solution on YOUR website!
the average of first 5 number s = 6, then total numbers = 6*5 = 30
similarly, total of 12 numbers = 7.5 *12 = 90
the total of last seven numbers = 90 - 30 = 60
and its average = 60/7 = 8.57
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