1.  A person purchases 90 clocks and sells 40 clocks at a gain of 10% and 50 clocks at a gain of 20%. If he sold all of them at a uniform profit of 15%, then he would have got ₹ 40 less. The cost price of each clock is:
A. ₹ 50
B. ₹ 60
C. ₹ 80
D. ₹ 90

Answer: Option C

Explanation:

Let C.P. of clock be ₹ x.

Then, C.P. of 90 clocks = ₹ 90x.

⇒ [(110% of 40x) + (120% of 50x)] - (115% of 90x) = 40

⇒ 44x + 60x - 103.5x = 40

∴ 0.5x = 40 => x = 80