1. **Problem statement:** The usual profit made by a jeweller on a watch is 35%. During a sale, 20% is taken off the market price. The watch was sold for 3672 during the sale. Find the cost price of the watch. 2. **Formula and explanation:** - Let the cost price be $C$. - Usual profit is 35%, so usual selling price $S = C + 0.35C = 1.35C$. - During the sale, 20% is taken off the market price (which is the usual selling price), so sale price $= 0.8 \times S = 0.8 \times 1.35C = 1.08C$. - Given sale price is 3672, so $1.08C = 3672$. 3. **Calculation:** $$ 1.08C = 3672 $$ Divide both sides by 1.08: $$ \cancel{1.08}C = \frac{3672}{\cancel{1.08}} $$ $$ C = \frac{3672}{1.08} = 3400 $$ 4. **Answer:** The cost price of the watch is 3400.