You don't need absolute numbers in this question, as it is ratio, it is enough if you know the ratio

Considering the number of men as 2x => # of women would be x

total weight/total number => (240X+150x)/(2x+x) =>130

Thus B alone is sufficient.

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In these kind of questions, it is sufficient to know one of the values, i.e in this specific case weight and number are the variables and weight is already given, and the ratio of numbers is sufficient.

Think of a scenario where weight and number both are given as ratios, then you will have two unknowns, i.e let us say the problem says the weight of men is twice the weight of women, the rest of the question being same, we will have

2y is the weight of men => y would be the weight of women

2x men and x women, thus (4xy+xy)/3x =>5y/3 thus it we need to know one of the values of the two unknowns in the questions of ratios to find out the absolute ratio.

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