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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote ## A bakery sold an average (arithmetic mean) of 820... tagged by: BTGmoderatorLU ##### This topic has 2 expert replies and 0 member replies ### Top Member ## A bakery sold an average (arithmetic mean) of 820... A bakery sold an average (arithmetic mean) of 820 cookies per day in an operating period. On "good" days, the bakery sold an average of 980 cookies per day, and on "fair" days, the bakery sold an average of 640 cookies per day. If every day in the operating period was either "good" or "fair", what was the ratio of the number of "good" days to the number of "fair" days for the bakery's operating period? A. 2:1 B. 3:2 C. 5:4 D. 7:6 E. 9:8 The OA is E. I'm really confused with this PS question. Experts, any suggestion about the solution? Thanks in advance. ### GMAT/MBA Expert GMAT Instructor Joined 04 Oct 2017 Posted: 551 messages Followed by: 11 members Upvotes: 180 Top Reply Quote: A bakery sold an average (arithmetic mean) of 820 cookies per day in an operating period. On "good" days, the bakery sold an average of 980 cookies per day, and on "fair" days, the bakery sold an average of 640 cookies per day. If every day in the operating period was either "good" or "fair", what was the ratio of the number of "good" days to the number of "fair" days for the bakery's operating period? A. 2:1 B. 3:2 C. 5:4 D. 7:6 E. 9:8 The OA is E. I'm really confused with this PS question. Experts, any suggestion about the solution? Thanks in advance. Hi LUANDATO, Let's take a look at your question. Let G be the number of good days and F be the number of fair days during the operating period, then Sum of Cookies during Good days + Sum of Cookies during Fair days = Sum of Cookies during the operating period ... (i) We know that, $$\text{Sum of quantities}=\left(Average\right)\left(\text{Number of Quantities}\right)$$ Therefore, we can write Eq(i) as: (Average cookies during good days)(Number of Good days) + (Average cookies during Fair days)(Number of fair days) = (Average Cookies during operating period)(Number of days in operating period) $$980G+640F=820\left(G+F\right)$$ $$980G+640F=820G+820F$$ $$980G-820G=820F-640F$$ $$160G=180F$$ $$\frac{G}{F}=\frac{180}{160}$$ $$\frac{G}{F}=\frac{9}{8}$$ Hence, the ratio of the number of "good" days to the number of "fair" days for the bakery's operating period is 9 : 8. Therefore, Option E is correct. Hope it helps. I am available if you'd like any follow up. _________________ GMAT Prep From The Economist We offer 70+ point score improvement money back guarantee. Our average student improves 98 points. Free 7-Day Test Prep with Economist GMAT Tutor - Receive free access to the top-rated GMAT prep course including a 1-on-1 strategy session, 2 full-length tests, and 5 ask-a-tutor messages. Get started now. ### GMAT/MBA Expert Elite Legendary Member Joined 23 Jun 2013 Posted: 10197 messages Followed by: 497 members Upvotes: 2867 GMAT Score: 800 Top Reply Hi LUANDATO, We're told that a bakery sold an average (arithmetic mean) of 820 cookies per day in an operating period. On "good" days, the bakery sold an average of 980 cookies per day, and on "fair" days, the bakery sold an average of 640 cookies per day. We're asked for the ratio of the number of "good" days to the number of "fair" days for the bakery's operating period. This question is essentially a 'Weighted Average', so here's how you can use that formula to answer the question: X = number of 'good' days Y = number of 'fair days (980X + 640Y)/(X+Y) = 820 980X + 640Y = 820X + 820Y 160X = 180Y 16X = 18Y 8X = 9Y X/Y = 9/8 Final Answer: E GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

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