A man bought a book for Rs.450 and sold for Rs.495. Find the gain percent.

\par S.P. = 495         \par C.P. = 450

\par Gain = 495 - 450 = 45                       $\lbrack gain = S.P - C.P.\rbrack $

\par Gain % =\frac{45}{450}$ $\times $ 100 = 10                    \par \lbrack gain % = \frac{Gain}{C.P.} \times 100\rbrack

\par \therefore$ gain % = 10