Multiple choice

The average weight of all the students in a certain class is 60 kg. The average weight of the boys from the class is 70 kg. While that of the girls is 55 kg. What is the ratio of number of boys to that of girls ?

  1. 2 : 1

  2. 1 : 2

  3. 1 : 4

  4. 4 : 1

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let B and G be the number of boys and girls, and W = B + G be total students. 60W = 70B + 55G. Substituting W = B + G: 60(B + G) = 70B + 55G, so 60B + 60G = 70B + 55G, giving 5G = 10B, or G = 2B. Therefore, B : G = 1 : 2.