Percent of a Number
Question
Answer choices
- 15
- 60
- 35
- 30
- 25
D Correct answer: D) 30
Set up the problem carefully before computing. Convert the percent to a decimal first; then multiply. 25/100 = 0.25, and 0.25 × 120 = 30.
Carry the arithmetic through one step at a time, double-checking signs and units. The ACT writes wrong answers to catch the most common slips, so an answer that "looks right" without verification is risky.
Plug the answer back into the original expression as a sanity check whenever the problem allows. If the substitution does not balance, you have made an arithmetic mistake earlier in the work.
The underlying rule
To find a percent of a number, multiply the number by the percent expressed as a decimal. 25% = 0.25, so 25% of 120 = 0.25 × 120 = 30.
Why each wrong answer is wrong
- A) 15: A common arithmetic or sign error leads to this value; carefully redo the calculation.
- B) 60: A common arithmetic or sign error leads to this value; carefully redo the calculation.
- C) 35: A common arithmetic or sign error leads to this value; carefully redo the calculation.
- E) 25: A common arithmetic or sign error leads to this value; carefully redo the calculation.
Study tip
Memorize: "of" means multiply, "percent" means divide by 100. Convert the percent to a decimal and multiply through.
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