Keats Library purchases a number of new books, all in the category of biography; the library does not acquire any other books. With the addition of the new biographies, the biography collection of the library amounts to 37.5% of the new total number of books in the library. If prior to the purchase, only 20% of the books in Keats Library were biographies, by what percent has the number of biographies in the library increased?	Options:
A) 17.5%
B) 62.5%
C) 87.5%
D) 140%
E) 150%
You are mixing a collection consisting of 20% biographies with a collection consisting of 100% biographies to give a collection consisting of 37.5% biographies. The weights of the two collections will be:   w1/w2 = (A2 - Avg)/(Avg - A1) = (1 - 3/8)/(3/8 - 1/5) = (5/8)/(7/40) = 25/7   So if initial collection had a total of 25 books (including 1/5th biographies i.e. 5 biographies), 7 new biographies were added.   Biographies have increased by (7/5)*100= 
<gadget id="calculator">(7/5)*100</gadget>
<output>140</output>
140%   Answer (140%)
<result>D</result>
Keats Library purchases a number of new books, all in the category of biography; the library does not acquire any other books. With the addition of the new biographies, the biography collection of the library amounts to 37.5% of the new total number of books in the library. If prior to the purchase, only 20% of the books in Keats Library were biographies, by what percent has the number of biographies in the library increased?