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The price of a laptop increased by 20% in the first month, then decreased by 10% in the second month, and increased again by 15% in the third month. If the original price of the laptop was ₹1,20,000, what is the final price after these three changes? 7 360
₹1,49,040
₹1,42,800
₹1,38,000
₹1,41,000
₹1,49,040
Use the multiplier method: 1.20×0.90×1.15=1.242. Simply multiply 1,20,000×1.242 to get the final result instantly.
Original price = ₹1,20,000. Changes: +20% (1st month), -10% (2nd month), +15% (3rd month).
Final Price=P×(1+100r1)×(1−100r2)×(1+100r3)
Use the multiplier method: 1.20×0.90×1.15=1.242. Simply multiply 1,20,000×1.242 to get the final result instantly.
Students often add the percentages (20 - 10 + 15 = 25%) instead of applying successive multipliers, leading to incorrect results like 1,50,000.
Calculate the cumulative multiplier
Convert the percentage changes into decimal multipliers: 1.20, 0.90, and 1.15. Multiply them together.
1.20×0.90×1.15=1.242
Apply the multiplier to the original price
Multiply the original price by the cumulative multiplier calculated in the previous step.
1,20,000×1.242=1,49,040
Verification of result
Checking the value against the options shows it matches Option A.
1,49,040
A is correct because applying the successive percentage changes of 20%, -10%, and 15% to 1,20,000 yields 1,49,040.
This logic is identical to calculating Compound Interest where the rates change annually; always use the multiplier method to save time in exam conditions.
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