Q.An article marked at ₹2,000 is sold for ₹1,700. Find the rate of discount.

The discount is the drop from marked price to selling price, expressed as a percentage of the marked price.

Here $MP=₹2{,}000$ and $SP=₹1{,}700$.

Step 1 — Find the discount amount.

Step 2 — Express it as a percentage of the marked price.

$\text{Discount}\%=\frac{\text{Discount}}{MP}\times100=\frac{300}{2000}\times100=15\%.$ …

Dividing the ₹300 discount by the selling price (₹1,700) instead of the marked price gives about $17.6\%$, which is wrong …