A book, originally priced at ₹600, is subject to a reduction in cost through two consecutive discounts: an initial markdown of 10%, followed by an additional 20% discount. The question then is to determine the conclusive selling price of the book once both these successive price adjustments have been applied.

Correct — A.
Apply the first discount: 10% off ₹600 = 600 × 0.9 = ₹540
Apply the second to the new price: 20% off ₹540 = 540 × 0.8 = ₹432

Check with the single equivalent discount: 10 + 20 − (10 × 20)⁄100 = 28%
Price left: 600 × 0.72 = ₹432

So the final selling price is ₹432 → option (a)

Why the others are wrong

• (b)
  ₹396 — ₹396 is 66% of ₹600, a combined cut of 34%. Successive discounts of 10% and 20% combine to 28%, leaving 72% of the price, ₹432.
• (c)
  ₹384 — This is 600 × 0.8 × 0.8, two 20% discounts in a row. The first discount here is 10%, so the first step leaves ₹540, not ₹480.
• (d)
  ₹350 — Lower than a flat 30% cut, which gives ₹420. Successive discounts of 10% and 20% take off less than 30% together, so the price cannot fall this far.

Successive discounts multiply; they do not add. The second discount is taken on the already reduced price, not on the original.

For discounts of x% and y%, the single equivalent discount is x + y − xy⁄100. For 10% and 20% that is 30 − 2 = 28%.

The order does not matter: 20% then 10% also leaves 0.8 × 0.9 = 0.72 of the price.

Key facts

• Two successive discounts x% and y% equal one discount of x + y − xy⁄100
• 10% and 20% in succession equal a single discount of 28%
• Swapping the order of two successive discounts does not change the final price

Common traps

• Taking the 20% off the original ₹600 (₹120) instead of off ₹540 (₹108), which lands on ₹420
• Multiplying by the discount (0.1, 0.2) instead of by what remains after it (0.9, 0.8)

No directly related past PYQ was found.