By selling a book for Tk.560, gain is as much percent as it costs in tk. The cost price is:

A Tk. 400

B Tk. 40

C Tk. 360

D Tk. 140

Correct Answer: Option E

Let, CP = x

so at x% gain, the SP = 100+x taka

now, the CP = 560 - (100+x)

= 660 - x

But, from the top, we know that,

660 - x = x

or, 660 = 2x

or, 660/2 = x

or, x = 330 taka