Equivalent mass in case of disproportionation reaction
I like and dislike the question. I assume this is from your Indian university entrance exams. The good part is that it is tricky, the sad part is that the concept of equivalents is so outdated that any North American student will barely recognize it. They should abolish teaching equivalents exactly because this problem you are encountering. 

Fact number no. 1, unlike molar equivalents of a given molecule equivalent weights are reaction dependent. Hence addition of equivalent weights is irrelevant. Equivalent weights are useful in analytical chemistry because they simplify calculations. The case of disproportionation reactions and their equivalents is rarely discussed because nobody uses disproportionation reactions in titrations, gravimetry etc.

In your case, you will have two equivalent weights one with respect to oxidation, and one respect to reduction. Solve the disporptionation reaction below and see what you get as an equivalent weight for $\ce{Br2}$ in each case.

$\ce{3Br2 + 6OH^- -&gt; 5Br^- + BrO3^- + 3H2O}$