Apply two or more percent changes in sequence.
Free, timed SHSAT practice sets on successive percent changes— every question includes a full worked explanation, and there's no account required.
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When a price changes twice, the second percent is taken of the new price, not the original. So you cannot just add or subtract the percents.
Change each percent into a multiplier and multiply them in order:
Example: 80 dollars goes down 25%, then up 20%: \(80 \times 0.75 \times 1.20 = 72\) dollars. Combining the changes into one 5% decrease gives 76 dollars, which is the trap answer.
Quick check: up 10% then down 10% does not bring you back to the start. \(100 \times 1.10 \times 0.90 = 99\), a 1% loss overall.
Order does not change the result (\(0.75 \times 1.20 = 1.20 \times 0.75\)), but the base for each step does: always apply the next percent to the newest price.
After the first change: \(\$36.00 \times (1 - 25/100) = \$27.00\). After the second change: \(\$27.00 \times (1 - 18/100) = \$22.14\). (Combining 25% and 18% into one 43% decrease of the original price gives $20.52. Stopping after the first change gives $27.00. Reporting only the total change in price (\(\$36.00 - \$22.14\)) gives $13.86.) The final price is $22.14.
After the first change: \(\$63.00 \times (1 - 20/100) = \$50.40\). After the second change: \(\$50.40 \times (1 + 15/100) = \$57.96\). (Combining 20% and 15% into one 5% decrease of the original price gives $59.85. Stopping after the first change gives $50.40. Applying only the second change to the original price gives $72.45.) The final price is $57.96.