1. Problem: A product's sale price at 20% discount is 480. Find its sale price at 20% profit value. Step 1: Let the marked price be $M$. Step 2: Sale price at 20% discount is $M - 0.2M = 0.8M = 480$. Step 3: Solve for $M$: $$M = \frac{480}{0.8} = 600$$. Step 4: Sale price at 20% profit is $M + 0.2M = 1.2M = 1.2 \times 600 = 720$. Answer: Rs 720. 2. Problem: A man sold a pen for Rs 180, which is Rs 60 less than what he paid. Find his loss percentage. Step 1: Cost price $C = 180 + 60 = 240$. Step 2: Loss = $C - 180 = 60$. Step 3: Loss percentage = $$\frac{60}{240} \times 100 = 25\%$$. Answer: 25%. 3. Problem: 3 liters of paint cover 24 m². Find percentage increase in paint quantity to cover 50.4 m². Step 1: Paint per m² = $$\frac{3}{24} = 0.125$$ liters. Step 2: Paint needed for 50.4 m² = $$50.4 \times 0.125 = 6.3$$ liters. Step 3: Increase in paint = $$6.3 - 3 = 3.3$$ liters. Step 4: Percentage increase = $$\frac{3.3}{3} \times 100 = 110\%$$. Answer: 110%. 4. Problem: Cost for hiring a car in 2018 was Rs 264, which is 20% more than in 2013. Find 2013 cost. Step 1: Let 2013 cost be $x$. Step 2: 2018 cost = $x + 0.2x = 1.2x = 264$. Step 3: Solve for $x$: $$x = \frac{264}{1.2} = 220$$. Answer: Rs 220. 5. Problem: Ali buys an oven for Rs 36800 and sells it at 8.5% gain. Find selling price. Step 1: Gain = $$0.085 \times 36800 = 3128$$. Step 2: Selling price = $$36800 + 3128 = 39928$$. Answer: Rs 39928.