Option 1 : Rs. 54

**Given**

The cost price of two watches is 90

The shopkeeper sold first watch at 20% profit and second at 10% loss in this he got total profit of 8%

**Formula used**

CP(1 + P/100) = SP

Here, CP = Cost Price

SP = Selling Price

P = Profit

**Calculation**

Let cp of first watch be Rs.x then cp of second watch be Rs( 90 - x)

⇒ x × 120/100 + (90 - x) × 90/100 = 90 × 108/100

⇒ 1.2 - 0.9x = 97.2 - 8

⇒ 0.3x = 16.2

⇒ x = 54

**∴ CP of first watch is Rs.54**

** **

Here 3x + 2x = 5x

⇒ 5x = 90

⇒ x = 18

⇒ 3x = 3 x 18

**∴ CP of first watch is Rs. 54**