SSC CGL Tier I 12 Sep 2025 Shift 2 Paper

Concept:The problem involves comparing original and swapped quantities. The price of a laptop is 5 times that of a desktop. Swapping the numbers increases the total cost by 80%, which gives an equation to find the unknown desktop count.Explanation:Let the number of desktops originally ordered be $x$.Let the price of one desktop be $₹p$. Then price of one laptop is $5p$.Original order: 20 laptops and $x$ desktops.Original bill: $20 \times 5p + x \times p = 100p + xp = p(100 + x)$.After mistake (quantities interchanged): $x$ laptops and 20 desktops.Wrong bill: $x \times 5p + 20 \times p = 5xp + 20p = p(5x + 20)$.The wrong bill is 80% more than the original bill, so it equals $1.8$ times the original bill:$$p(5x + 20) = 1.8 \times p(100 + x)$$Cancel $p$ (non-zero): $5x + 20 = 1.8(100 + x)$.Expand: $5x + 20 = 180 + 1.8x$.Rearrange: $5x - 1.8x = 180 - 20 \Rightarrow 3.2x = 160$.Solve: $x = 160 / 3.2 = 50$.Original ratio of laptops to desktops = $20 : 50 = 2 : 5$.Answer:The required ratio is $2:5$, which corresponds to option D.