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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 ## If each year the population of the country tagged by: NandishSS ##### This topic has 1 expert reply and 0 member replies ## If each year the population of the country If each year the population of the country grows by 20%, how many years will elapse before the population of the country doubles? A. 3 B. 4 C. 5 D. 6 E. 7 OA: B ### GMAT/MBA Expert Legendary Member Joined 20 Jul 2017 Posted: 503 messages Followed by: 10 members Upvotes: 86 GMAT Score: 770 If the population of the country grows by 20% each year, the population the next year will be 120% of the year before, or $$1.2\cdot previous\ population$$ For each year, we'll multiply by 1.2 again. So after one year, the population will be $$1.2\cdot original\ population$$ After two years, the population will be $$1.2\cdot1.2\cdot original\ population=1.44\cdot original\ population$$ After three years, the population will be $$1.44\cdot1.2\cdot original\ population=1.728\cdot original\ population$$ After four years, the population will be $$1.728\cdot1.2\cdot original\ population=2.0736\cdot original\ population$$ We want to find how many years it will take to double the population, or $$2\cdot original\ population$$ The population has slightly more than doubled after 4 years, so the answer is B. Note: we could also express the equation for the country's population as $$1.2^x\cdot original\ population$$ where x is the number of years that have elapsed. Then we can set this equal to our expression for doubling the population: $$1.2^x\cdot original\ population=2\cdot original\ population$$ $$1.2^x=2$$ and then solve for x. _________________ Erika John - Content Manager/Lead Instructor https://gmat.prepscholar.com/gmat/s/ Get tutoring from me or another PrepScholar GMAT expert: https://gmat.prepscholar.com/gmat/s/tutoring/ Learn about our exclusive savings for BTG members (up to 25% off) and our 5 day free trial Check out our PrepScholar GMAT YouTube channel, and read our expert guides on the PrepScholar GMAT blog • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • FREE GMAT Exam Know how you'd score today for$0

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