Question:
A student buys a pen for Rs 90 and sells it for Rs 100. Find his gain and gain percent.
Solution:
C. $\mathrm{P}$ of pen $=$ Rs. 90
S.P of pen $=$ Rs. 100
Gain $=\mathrm{SP}-\mathrm{CP}$
Gain $=100-90$
$=$ Rs. 10
Gain $\%=\left(\frac{\text { gain } \times 100}{\text { C.P. }}\right)$
$=\left(\frac{10 \times 100}{90}\right)$
$=11 \frac{1}{9} \%$