![\"Manhattan](\"\/\/cdn2.manhattanprep.com\/gmat\/wp-content\/uploads\/sites\/18\/2018\/03\/more-fast-math-for-the-gmat-part-7-stacey-koprince.png\")
<\/p>\n<\/p>\n
Guess what?\u00a0You can attend the first session of any of our online or in-person GMAT courses absolutely free\u2014we\u2019re not kidding!\u00a0Check out our upcoming courses here<\/a>.<\/em><\/strong><\/span><\/p>\n A while back, we started a series on Fast Math for the GMAT\u2014here\u2019s the <\/span>link<\/span><\/a> if you want to start from the beginning.<\/span><\/p>\n In our last installment, I gave you two problems to try. We\u2019ve already discussed the first one; here\u2019s the second one again (from the free problem set on mba.com<\/a><\/span>).<\/span> The Earth travels around the Sun at a speed of approximately 18.5 miles per second. This approximate speed is how many miles per hour?<\/span><\/p>\n (A) 1,080<\/span><\/p>\n (B) 1,160<\/span><\/p>\n (C) 64,800<\/span><\/p>\n (D) 66,600<\/span><\/p>\n (E) 3,996,000<\/span><\/p>\n What do you think?<\/span><\/p>\n \u00a0<\/p>\n Step 1: Understand<\/p>\n Those answers\u2026they are seriously far apart. The first two are \u201cclumped,\u201d then the next two, and that last one is totally different.<\/span><\/p>\n We\u2019re definitely going to estimate on this one. \u263a Also, just from glancing at the answers, I\u2019m guessing that the correct answer will not be (E). Chances are pretty good that the correct answer will have another \u201cclose\u201d answer based on making some small mistake\u2014or based on making the problem just a little harder to estimate.<\/span><\/p>\n Jot down the details.<\/span><\/p>\n \u00a0<\/p>\n Step 2: What\u2019s the plan?<\/span><\/p>\n How do you go from seconds to hours?<\/span><\/p>\n 60 seconds \u2192 1 minute<\/span><\/p>\n 60 minutes \u2192 1 hour<\/span><\/p>\n So we need 60 twice. But is that\u2026multiplying? Dividing? Glance at the answers again or think it out logically. All of the answers are greater than 18.5, so I must have to multiply. And logically, that makes sense: If I go 18.5 miles in one second, then I should be able to go a lot further in a whole hour.<\/span><\/p>\n Okay, now which \u201cclump\u201d of answers is the right clump? 18.5 is a really annoying number, but the clumps are so far apart that I can just call that 20 for now.<\/span><\/p>\n (20)(60) = 1,200<\/span><\/p>\n Hmm. I still need to multiply by another 60, so answers (A) and (B) are out.<\/span><\/p>\n But I\u2019m only multiplying by another 60, so answer (E) is out, too. It\u2019s down to (C) and (D).<\/span><\/p>\n If I just multiply by another 60 now\u2026will it be close enough? I\u2019m not sure. I overestimated (from 18.5 to 20) and the two final numbers are pretty close. If the answer is (C), I might think it\u2019s (D) just from the error I introduced in my estimation.<\/span><\/p>\n In fact, (1,200)(60) = 72,000. Definitely not good enough. Okay, what should I do next?<\/span><\/p>\n The \u201cofficial\u201d math is this:<\/span><\/p>\n (18.5)(60)(60)<\/span><\/p>\n The math that I actually did was this:<\/span><\/p>\n (20)(60)(60)<\/span><\/p>\n Hmm. So I overestimated because I used 20 rather than 18.5. In other words, I overestimated by 1.5\u2014times 60 times 60:<\/span><\/p>\n (1.5)(60)(60) = overestimate<\/span><\/p>\n The latter two are easy: (60)(60) = 3,600. Oh, and then multiplying by 1.5 is the same thing as increasing something by 50%. So 3,600 + half of 3,600 = 3,600 + 1,800 = 5,400.\u00a0<\/span><\/p>\n My original \u201canswer\u201d was 72,000 but I overestimated by 5,400.<\/span><\/p>\n 72,000 minus 5,000-ish, is about 67,000. The actual value should be a little less, since I actually want to subtract 5,400. The answer must be (D) 66,600. Answer (C) is too small.<\/span><\/p>\n (1) If you think you need to do long division or long multiplication, stop for a moment. Reflect. Even if you have to do partial long division or multiplication, how much do you <\/span>really<\/span><\/i> have to do?<\/span><\/p>\n (2) As we discussed last time, don\u2019t start solving on PS until you\u2019ve looked at those answer choices! Sometimes, they contain very important clues about the most efficient way to solve.<\/span><\/p>\n Can\u2019t get enough of Stacey\u2019s GMAT mastery? Attend the first session of one of\u00a0her upcoming GMAT courses<\/a>\u00a0absolutely free, no strings attached. Seriously.<\/strong><\/em><\/p>\n Guess what?\u00a0You can attend the first session of any of our online or in-person GMAT courses absolutely free\u2014we\u2019re not kidding!\u00a0Check out our upcoming courses here. A while back, we started a series on Fast Math for the GMAT\u2014here\u2019s the link if you want to start from the beginning. In our last installment, I gave you […]<\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[873,929,52871,930,2,8,9],"tags":[53022,53023],"yst_prominent_words":[57273,57276,57270,54235,53868,57277,57271,54040,57278,57281,53781,57274,57272,57280,57275,57269,57279,53784,53867],"class_list":["post-15323","post","type-post","status-publish","format-standard","hentry","category-for-current-studiers","category-gmat-prep","category-gmat-strategies","category-gmat-study-guide","category-how-to-study","category-quant-on-gmat","category-taking-the-gmat","tag-fast-math","tag-fast-math-for-the-gmat"],"_links":{"self":[{"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/posts\/15323","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=15323"}],"version-history":[{"count":6,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/posts\/15323\/revisions"}],"predecessor-version":[{"id":19598,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/posts\/15323\/revisions\/19598"}],"wp:attachment":[{"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/media?parent=15323"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/categories?post=15323"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/tags?post=15323"},{"taxonomy":"yst_prominent_words","embeddable":true,"href":"https:\/\/www.manhattanprep.com\/gmat\/wp-json\/wp\/v2\/yst_prominent_words?post=15323"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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\n<\/p>\n![\"Manhattan](\"https:\/\/www.manhattanprep.com\/gmat\/wp-content\/uploads\/sites\/18\/2018\/01\/quant-process-1.png\")
<\/p>\n![\"\"](\"https:\/\/www.manhattanprep.com\/gmat\/wp-content\/uploads\/sites\/18\/2018\/03\/fast-math-part-7-image-1.png\")
<\/p>\n![\"Manhattan](\"https:\/\/www.manhattanprep.com\/gmat\/wp-content\/uploads\/sites\/18\/2018\/01\/quant-process-2.png\")
<\/p>\nKey Fast Math Takeaways:<\/b><\/h4>\n
* GMATPrep<\/span>\u00ae<\/span> questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.<\/span><\/h6>\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>\u00a0Stacey has been teaching the GMAT, GRE, and LSAT for 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.\u00a0Check out Stacey\u2019s upcoming GMAT courses here<\/a>.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"