Question

Tick (✓) the correct answer:
If the selling price of 10 pens is the same as the cost price of 12 pens then gain per cent is
(a) 2%
(b) 12%
(c) 20%
(d) 25%

Answer 1

(c) 20%

$$\begin{gathered} \mathrm{Let}\mathrm{Rs}x\mathrm{be}\mathrm{the}\mathrm{SP}\mathrm{of}\mathrm{each}\mathrm{pen}. \\ \mathrm{SP}\mathrm{of}10\mathrm{pens}=\mathrm{CP}\mathrm{of}12\mathrm{pens}=\mathrm{Rs}12x \\ \mathrm{CP}\mathrm{of}10\mathrm{pens}=\mathrm{Rs}10x \\ \mathrm{Now},\mathrm{gain}=\mathrm{Rs}\left(12\mathrm{x}-10\mathrm{x}\right) \\ =\mathrm{Rs}2x \\ \therefore \mathrm{Gain}\mathrm{percentage}=\left(\frac{\mathrm{gain}}{\mathrm{CP}}\times 100\right)\% \end{gathered}$$
$$\begin{gathered} =\left(\frac{2x}{10x}\times 100\right)\% \\ =20\% \end{gathered}$$