A wholesaler sells a watch to a retailer at a gain of 20% and the retailer sells it to a customer at a loss of 10%. If the customer pays Rs 874.8, what had it cost the wholesaler?

For the wholesaler,

Let the cost price = Rs. $$100x$$

With profit of 20%, Selling price = $$\frac{120}{100} \times 100x = Rs. 120x$$

For the retailer,

Cost price = Rs. $$120x$$

With a loss of 10%, Selling price = $$\frac{90}{100} \times 120x = Rs. 108x$$

For the customer,

Cost price = $$108x = 874.8$$

=> $$x = \frac{874.8}{108} = \frac{97.2}{12} = 8.1$$

$$\therefore$$ Cost price for retailer = $$100 \times 8.1 = Rs 810$$