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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 ## The ratio of local and international calls made by Amy... tagged by: AAPL ##### This topic has 3 expert replies and 0 member replies ### Top Member ## The ratio of local and international calls made by Amy... The ratio of local and international calls made by Amy this week is 5 to 2. If the ratio changes to 5 to 3 after Amy makes three more international calls, how many local calls did Amy make this week? A. 3 B. 5 C. 10 D. 15 E. 21 The OA is D. Local international ratio 5x/2x. Then local international ratio 5x/3x. Can I say $$\frac{5}{3}=\frac{5x}{2x+3}$$ and solve for x? I don't have clear this PS question. I appreciate if any expert explains it to me. Thank you so much. ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 12435 messages Followed by: 1244 members Upvotes: 5254 GMAT Score: 770 AAPL wrote: The ratio of local and international calls made by Amy this week is 5 to 2. If the ratio changes to 5 to 3 after Amy makes three more international calls, how many local calls did Amy make this week? A. 3 B. 5 C. 10 D. 15 E. 21 Let L = number of local calls made this week Let N = number of international calls made this week The ratio of local and international calls made by Amy this week is 5 to 2 So, L/N = 5/2 Cross multiply to get: 2L = 5N The ratio changes to 5 to 3 after Amy makes three more international calls So, now N+3 = number of international calls made this week And L still equals number of local calls made this week We can write: L/(N + 3) = 5/3 Cross multiply to get: 3L = 5(N + 3) Expand to get: 3L = 5N + 15 We know have the following system of equations 3L = 5N + 15 2L = 5N SUBTRACT the bottom equation from the top equation to get: L = 15 Answer: D Cheers, Brent _________________ Brent Hanneson â€“ Creator of GMATPrepNow.com Use our video course along with Sign up for our free Question of the Day emails And check out all of our free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert Legendary Member Joined 14 Jan 2015 Posted: 2667 messages Followed by: 121 members Upvotes: 1153 GMAT Score: 770 AAPL wrote: The ratio of local and international calls made by Amy this week is 5 to 2. If the ratio changes to 5 to 3 after Amy makes three more international calls, how many local calls did Amy make this week? A. 3 B. 5 C. 10 D. 15 E. 21 The OA is D. Local international ratio 5x/2x. Then local international ratio 5x/3x. Can I say $$\frac{5}{3}=\frac{5x}{2x+3}$$ and solve for x? I don't have clear this PS question. I appreciate if any expert explains it to me. Thank you so much. You could also back-solve and use a little logic. First, we know that local calls must be a multiple of 5, so only B, C, and D are options. Next, we can see quickly that B doesn't make sense - if there had been exactly 5 local calls and 2 international calls, if 3 more international calls had been made, the ratio would have been 5:5, not 5:3. B is out. Now we just have to test one of the two remaining answer choices. If it works, it's our answer. If it doesn't, the other is our answer. If there had been 10 local calls, then there'd have been 4 international calls. (10:4 = 5:2.) If there'd been 3 more international calls, the ratio would have been 10:7. We want 5:3. So C is out. We're left with D _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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### GMAT/MBA Expert

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AAPL wrote:
The ratio of local and international calls made by Amy this week is 5 to 2. If the ratio changes to 5 to 3 after Amy makes three more international calls, how many local calls did Amy make this week?

A. 3
B. 5
C. 10
D. 15
E. 21
The ratio of local to international calls is 5x : 2x. Since after three more international calls are made, resulting in a new ratio of 5 to 3, we can create the equation:

5x/(2x + 3) = 5/3

15x = 5(2x + 3)

3x = 2x + 3

x = 3

So Amy made 5(3) = 15 local calls this week.

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Scott Woodbury-Stewart Founder and CEO

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