Question 843041
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