AccelePrep for the ACT Test 2nd Edition Student Text

102 • S URGE TO S UCCESS ! M ATH T EST P REP

9. To avoid dividing when you ought to be multiplying, be sure to include your units: . $ . . $ . $ . $ . $ . 3 5 2 80 3 5 2 66 9 80 9 31 19 11 lbs lb lbs lb : : , (E). ‘–‹…‡ –Šƒ– ›‘—” DzŽ„dz —‹–•…ƒ…‡ŽǤ † ›‘—” ϐ‹ƒŽ ƒ•™‡” ‹• ‡š’”‡••‡† in units of “dollars,” which is exactly how you would answer the question “What is the total cost?” 10. Since you are asked, “How long, in minutes, will it take the printer to produce p ’ƒ‰‡•ǡdz ›‘—” ϐ‹ƒŽ ƒ•™‡” •Š‘—Ž† „‡ ‹ –‡”• ‘ˆ ‹—–‡•Ǥ —– do you multiply, add and multiply, or multiply and divide—and using what values? Watch what happens if we use units: F. pxt = (pages)(pages)(minutes) = (pages 2 )(minutes) That is not a unit that makes any sense. You’d never, ever say to someone, “Give me three pages-squared-minutes.” What about (G)? You run into the same problem. And (H)? You’d have minutes pages pages ^ ^h h . ‘•‡•‡Ǥ ‘‘ ƒ– ȋ Ȍǣ pages minutes pages ^ h . Here, “pages” cancels out and you are left with minutes 1 . Is minutes 1 an answer to the question “How long?” Obviously not. The correct answer must be (K). Indeed, pages pages minutes minutes ^ h . The “pages” in the numerator and “pages” in the denominator cancel, leaving only “minutes.” And the question asks, “How many minutes?” so we have found our answer.