find the average of 7/8, 9/20

Question

Im wondering how to you do the problem

 

Answer 1

The average of any set of numbers is the sum of them divided by the number of numbers in the set.

 

The sum of those numbers is

 

7/8 + 9/20 

 

Find the common denominator by multiplying the denominators together

 

(7*20 + 9*8) / (20*8) = (140 + 72) / (160) = 212/160 

 

Now simplify that to get 53/40

 

Remember that the average was the sum divided by the number of numbers (2, in this case).

 

(53/40) / 2 = (53/40) / (2/1)

 

The rule for dividing by a fraction is to multiply by its reciprocal.

 

(53/40) * (1/2) = 53/80