There are two divisions A and B of a class, consisting of 36 and 44 students respectively. If the average weight of divisions A is 40 kg and that of division b is 35 kg. What is the average weight of the whole class?
38.25
37.25
38.5
37
Explanation:
Total weight of students in division A = $ 36 \times 40$
Total weight of students in division B = $ 44 \times 35$
Total students = 36 + 44 = 80
Average weight of the whole class
$= \dfrac{\left(36 \times 40\right)+\left(44 \times 35\right)}{80} $
$= \dfrac{\left(9 \times 40\right)+\left(11\times 35\right)}{20} $
$= \dfrac{\left(9 \times 8\right)+\left(11\times 7\right)}{4} $
$= \dfrac{72+77}{4}\\$
$= \dfrac{149}{4}\\$
=$37.25$