Question

if the cost price 12 pencil is equal to the selling price of 15 pencil, then the loss percent is?

Answer 1

Friends, we know we will need gain amount to get gain percent, right. So lets get gain first.

Let the cost price of 1 pen is Re 1 
Cost of 8 pens = Rs 8
Selling price of 8 pens = 12
Gain = 12 - 8 = 4

\begin{aligned} 
Gain\% = \left( \frac{Gain}{Cost} * 100 \right)\% \\ 
= \left( \frac{4}{8} * 100 \right)\% = 50\% 
\end{aligned}