Total of weights should be W1+W2 .. Why it is written 100 then, please explain the question and the solution..

The question is the second picture i.e the example and the solution is above it..

Bcoz index is supposed as R and weight is supposed as W. The amount of weight is not given and supposed as W1 and W2 therefore, the amount of RW will be 100 W1 and 125 W2

Thanks neha! Got it.. =)