Report the amount of change when the final value is asked, or vice versa.
An error-pattern drill: practice spotting and avoiding this specific SHSAT trap.
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An 80-dollar jacket is 25% off. What is the sale price? 25% of 80 is 20 dollars, and many students stop and choose 20. But 20 dollars is the discount. The sale price is \(80 - 20 = 60\) dollars.
The trap works because finding the percent is the hard step, so it feels like the end. The test almost always lists both the change and the new amount.
Check habits:
Sale price \(= \$110.00 \times (1 - 45/100) = \$60.50\). (Reporting only the 45% discount instead of the sale price gives $49.50. Adding the 45% instead of subtracting it gives $159.50. Subtracting \(\$45\) instead of 45% gives $65.00.) The sale price is $60.50.
New price \(= \$24.00 \times (1 + 48/100) = \$35.52\). (Reporting only the 48% change instead of the new price gives $11.52. Subtracting the 48% instead of adding it gives $12.48. Adding \(\$48\) instead of 48% gives $72.00.) The new price is $35.52.
Simple interest \(I = P r t = \$1000.00 \times 3/100 \times 3 = \$90.00\); balance \(= P + I = \$1090.00\). (Forgetting to multiply by the number of years gives $30.00. Adding the interest to the deposit (the balance) gives $1090.00. Using \(0.3\) instead of \(0.03\) for the rate gives $900.00.) The interest earned is $90.00.