Let the initial number of books be X out of which A are biographies.

Given : A/X = 20% or 1/5 . Hence A = X/5

Let the new no of biographies added be Y.

Given (A+Y)/(X+Y) = 37.5% or 3/8 which gives Y = (7/25)X

Hence increase in biographies = Y/X = 7/5 or **140%**

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