Answer:
18 1/2 or 37/2
Step-by-step explanation:
To calculate the average of something, we add the numbers and divide by the count of those numbers. In this case, we have this as the sum of the numbers:
9 × 20 + 4 × 19 + 3 × 18 + 5 × 17 + 12
And the number of students as the count:
9 + 4 + 3 + 5 + 1
Now to calculate that out:
(9 × 20 + 4 × 19 + 3 × 18 + 5 × 17 + 12)/(9 + 4 + 3 + 5 + 1) ⇒
(180+76+54+85+12)/(9+4+3+5+1) ⇒
407/22 ⇒
37/2⇒
18 1/2
