Option 1 : Rs. 500, Rs. 400

**Given:**

Amar purchase two laptops in Rs. 900.

He sells one of them at a loss of 10%

And another one at a gain of 15%.

**Calculation:**

Let the cost price of 1^{st} laptop be Rs. x

And the cost price of 2^{nd }laptop be Rs. (900 – x)

10% loss = 1/10 and 15% profit = 3/20

According to question:

(3/20) × (900 – x) – (1/10) × x = 10

⇒ 2700 – 5x = 200

⇒ 5x = 2500

⇒ x = Rs. 500

Hence, the cost price of 1^{st} laptop = Rs. 500

Then, cost price of 2^{nd }laptop = Rs. (900 – 500) = Rs. 400

**∴ The cost price are Rs. 500 and Rs. 400 respectively.**

Let the CP of 1st laptop be Rs. x

Let the CP of 1st laptop be Rs. y

According to the question,

x + y = 900 ----(1)

Overall gain, Rs. 10, and Total CP = 900

Overall gain% = (gain/Total CP) × 100

⇒ (10/900) × 100 = 10/9%

By alligation method,

⇒ 5 : 4

Now, CP of 1st laptop = Rs. x = 5k

CP of 2nd laptop = Rs. y = 4k

From eq(1):

⇒ 5k + 4k = 900

⇒ 9k = 900

⇒ k = 100

The cost price of 1st laptop = Rs. 5K = 5 × 100 = Rs. 500

The cost price of 2^{nd} laptop = Rs. 4k = 4 × 100 = Rs. 400