The price of a pen was twice that of a pencil. One person ordered 4 pens and some pencils. At the time of preparing the bill, the prices of these articles interchanged. This increased the bill by 50%. The ratio of number of pens to the number of pencils was

Let price of each pencil = Rs. $$x$$ and price of each pen = Rs. $$2x$$

Let number of pencils ordered = $$y$$ and number of pens ordered = $$4$$

=> Original cost price = Rs. $$(xy+8x)$$

After interchanging the price, => New price of bill = Rs. $$(4x+2xy)$$

According to ques,

=> $$\frac{4x+2xy}{xy+8x}=1.5$$

=> $$4x+2xy=1.5xy+12x$$

=> $$4+2y=1.5y+12$$

=> $$0.5y=12-4=8$$

=> $$y=\frac{8}{0.5}=16$$

$$\therefore$$ Ratio of pens to pencils = $$\frac{4}{16}=1:4$$

=> Ans - (B)