Answer & Solution
Answer: Option C
Solution:
$$\eqalign{
& \text{B} = \frac{40 + 30 + 50}{3} = \frac{120}{3} = 40 \cr
& \text{C} = \frac{20 + 40 + 20}{3} = \frac{80}{3} \cr
& \text{then B : C} = 40 : \frac{80}{3} \cr
& \,\,\,\,\,\,\,\,\, \text{B : C} = 3 : 2 \cr} $$