![\"Manhattan](\"http:\/\/www.manhattanprep.com\/gmat\/wp-content\/uploads\/sites\/18\/2017\/05\/fast-math-gmat-part-3-stacey-koprince.png\")
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Did you know that you can attend the first session of any of our online or in-person GMAT courses absolutely free? We\u2019re not kidding! <\/i><\/b>Check out our upcoming courses here<\/i><\/b><\/a>.<\/i><\/b><\/span><\/p>\n Welcome to the third installment of our Fast Math series. (Miss the earlier installments? Start here.<\/a>)<\/span><\/p>\n Here\u2019s the basic premise: I\u2019m always on the lookout for ways to get out of doing tedious paper calculations on the GMAT. <\/span><\/p>\n The awesome part: The test writers actually set this up for me! They know we\u2019re not going to have to do a bunch of paper math in b-school or the real world, so they construct problems that allow us to take advantage of all sorts of shortcuts\u2026<\/span>if<\/span><\/em> we\u2019re paying attention.<\/span> Some GMAT problems appear to involve tedious percent calculations, but they\u2019re really not all that tedious if you take a step back and use benchmarks.<\/span><\/p>\n What are benchmarks? First, let\u2019s start with a number<\/span>\u23af<\/span>say, 140. Now, let\u2019s say that the problem calls for 18% of 140. You could set up a couple of fractions and then simplify numerators and denominators\u2026but ugh.<\/span><\/p>\n Here\u2019s how to use benchmarks instead:<\/span><\/p>\n The starting number, 140, is 100%.<\/span><\/p>\n 10% of 140 is 14. Therefore, 20% is twice that, or 28.<\/span><\/p>\n You\u2019re trying to get to 18%, which is 2% less then 20%.<\/span><\/p>\n Since 20% = 28, it\u2019s the case that 2% = 2.8.<\/span><\/p>\n 20% \u2212 2% = 18%, so 28 \u2212 2.8 = 25.2.<\/span><\/p>\n That\u2019s it! The answer is 25.2<\/span><\/p>\n Any<\/span><\/i> percentage can be calculated using some combination of \u201cbenchmark\u201d percentages that are easier to find. The easiest-to-find benchmarks are 100%, 50%, 10%, and 1% of your original number. And from 50%, you can move the decimal left once to get 5%. Using these 5 benchmarks, you can calculate anything, because you can \u201cadd up\u201d percents.<\/span><\/p>\n For example, find 63% of 86.<\/span><\/p>\n 63% = 50% + 10% + 3(1%)<\/span><\/p>\n 50% of 86 is 43<\/span><\/p>\n 10% of 86 is 8.6<\/span><\/p>\n 1% of 86 is 0.86 (and we need 3%, so it\u2019s really 3 <\/span>\u00d7<\/span> 0.86)<\/span><\/p>\n Don\u2019t add those all up right now. Glance at the answer choices to see whether you can estimate from here. This is the GMAT, so it might just be enough to estimate low 50s. If I\u2019m really pressed, I might go as far as, \u201cIt\u2019s 51.6 plus a little less than 3, so around 54.\u201d On the GMAT, that\u2019ll be enough to get to the answer.<\/span><\/p>\n Practice that benchmarking until you can do it in your sleep (well, until you can do it at the restaurant table while estimating an 18% tip). And join us next time<\/a>, when we\u2019ll cover Principle #4!<\/span><\/p>\n KEEP READING:<\/strong> FAST Math for the GMAT (Part 4)<\/a><\/p>\n Can\u2019t get enough of Stacey\u2019s GMAT mastery? Attend the first session of one of her upcoming GMAT courses<\/a> absolutely free, no strings attached. Seriously.\u00a0<\/strong><\/em><\/p>\n Did you know that you can attend the first session of any of our online or in-person GMAT courses absolutely free? We\u2019re not kidding! Check out our upcoming courses here. Welcome to the third installment of our Fast Math series. (Miss the earlier installments? Start here.) Here\u2019s the basic premise: I\u2019m always on the lookout […]<\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[873,18,929,52871,930,2,8],"tags":[53022,53023],"yst_prominent_words":[55251,57239,57240,57235,54388,57241,54095,57236,57238,53868,57237,53653,53779,57221,53877,53635,53781,53775,53784,53867],"class_list":["post-13731","post","type-post","status-publish","format-standard","hentry","category-for-current-studiers","category-manhattan-gmat-blog-fdp","category-gmat-prep","category-gmat-strategies","category-gmat-study-guide","category-how-to-study","category-quant-on-gmat","tag-fast-math","tag-fast-math-for-the-gmat"],"_links":{"self":[{"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/posts\/13731","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/comments?post=13731"}],"version-history":[{"count":8,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/posts\/13731\/revisions"}],"predecessor-version":[{"id":19607,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/posts\/13731\/revisions\/19607"}],"wp:attachment":[{"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/media?parent=13731"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/categories?post=13731"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/tags?post=13731"},{"taxonomy":"yst_prominent_words","embeddable":true,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/yst_prominent_words?post=13731"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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\n<\/p>\nPrinciple #3: Use benchmarks to find percents<\/b><\/h4>\n
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\n![\"stacey-koprince\"](\"https:\/\/cdn2.manhattanprep.com\/gmat\/wp-content\/uploads\/sites\/18\/2015\/06\/stacey-koprince-150x150.png\")
<\/a>Stacey Koprince<\/a> is a Manhattan Prep instructor based in Montreal, Canada.<\/strong> Stacey has been teaching the GMAT, GRE, and LSAT \u00a0for more than 15 years and is one of the most well-known instructors in the industry. Stacey loves to teach and is absolutely fascinated by standardized tests. Check out Stacey\u2019s upcoming GMAT courses here<\/a>.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"