Explanation:

- Step 1: Understanding the problem

P sold a phone to Q at a profit of 25%. Q sold it to R at a loss of 10%. R paid Rs 3240.

- Step 2: Calculate Q's selling price to R

Since Q sold the phone at a loss of 10%, this means R bought it for 90% of Q's cost.

$$

Q's \text{ cost price} = 3240 / 0.9 = 3600

$$

- Step 3: Calculate P's original price

P sold the phone to Q at a 25% profit, which means Q bought it for 125% of P's cost.

$$

P's \text{ original price} = 3600 / 1.25 = 2880

$$

- Options Review

- Option 1: Rs 3,000

- Option 2: Rs 2,880

- Option 3: Rs 3,600

- Option 4: Rs 2,580

- Conclusion:

The price paid by P was Rs 2,880.