How many Elements are there in Set B?

Question

The average in Set A is 85, and the average in Set B is 65. If the combined average of all elements in Set A AND B is 70, and Set A has 5 Elements, how many elements are in Set B?

 

What do I do to solve the problem?? How do I solve the problem?

Answer 1

You must know the meaning of "average" and how to express it algebraically.

 

Set A has 425 (5 x 85)

Set B has 65x 

 

(Set A + Set B) / (5 + x) = 70

(425 + 65x) / (5 + x) = 70

425 + 65x = 70(5 + x)

425 + 65x =350 + 70x

75 = 5x

15 = x