Calculating average

Question

The average score for a class of 25 students was 75. If the 15 female students in the class averaged 70, then the male students in the class averaged:

a.	85.0
b.	82.5
c.	77.5
d.	75.0
e.	70.0

Answer 1

average = total sum of scores / number of scores:

15*70 + 10*x = 75

-----------------

25

15*70 + 10*x = 1875

10x = 825

x = 82.5 (b)

Answer 2

Average = Sum of terms / number of terms.

Therefore, Sum of terms = Average* number of terms.

If the average of 25 students is 75, then the sum of the scores is 25* 75 = 1875

The sum of the scores = sum of female scores + sum of male scores.

The sum of female scores is the number of females * average of female scores = 15 * 70 = 1050

The sum of male scores is the number of males * average of male scores = 10 * average of male scores.

Plugging into the equation: The sum of the scores = sum of female scores + sum of male scores gives

1875 = 1050 + 10 * average of male scores.

Now just solve for the average of male scores.