IB Mathematics SL Prep

Category - IB Mathematics

Brian is opening a small sporting goods store. After considering her market, she sets her initial sales goal at $32,000 a month. He knows that the rent for his store should be about 8% of sales. Approximately what should he plan to pay for rent, based on the sales figure given?
  1. $2,400
  2. $2,560
  3. $3,200
  4. $3,260
  5. $3,305
Explanation
Answer: 8% of $32,000 is $2,560.

A mental shortcut for multiplying by 8 is to multiply the number by 10, then subtract the original number twice. In this example, multiply 32,000 by 10, which equals 320,000. Then subtract 32,000 twice (320,000 - 32,000 = 288,000; 288,000 - 32,000 = 256,000).

Remember, that you are considering 8 percent, so move the decimal point two places to the left, to reach an answer of $2,560. We know this is a reasonable answer because 10% of $32,000 would be $3,200, so the answer is only slightly less than that.

Key Takeaway: It is easy to calculate percentages that are near 10%. To multiply by seven
(to find 7% of a number), for example, you would multiply by 10, then subtract the original number three times. To multiply by twelve (to find 120%), you would multiply by 10, then add the original number twice.
Was this helpful? Upvote!
Login to contribute your own answer or details

Top questions

Related questions

Most popular on PracticeQuiz