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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 ## Tough Geometry Problem tagged by: Brent@GMATPrepNow ##### This topic has 1 expert reply and 3 member replies ## Tough Geometry Problem 2 persons start walking on a road that diverge at an angle of 120 degree. if they walk at rate 3 km/h and 2 km/h respectively. Find the distance between them after 4 hours. a. 5 km 2. 4âˆš19 km c. 7 km d. 8âˆš19 km e. None of these Master | Next Rank: 500 Posts Joined 08 Feb 2011 Posted: 436 messages Followed by: 6 members Upvotes: 72 vikrantr93 wrote: 2 persons start walking on a road that diverge at an angle of 120 degree. if they walk at rate 3 km/h and 2 km/h respectively. Find the distance between them after 4 hours. a. 5 km 2. 4âˆš19 km c. 7 km d. 8âˆš19 km e. None of these CosC= a^2+b^2-c^2/2ab; here angle C=120; a=12; b=8;c=?? (as two persons are traveling at the speed of 3 and 2km/h, therefore distance covered in 4 hours will be 3*4=12 and 2*4=8) Cos 120=-1/2; -1/2=144+64-c^2/2 12*8; c^2=304; c=4sqrt(19) hence B; _________________ O Excellence... my search for you is on... you can be far.. but not beyond my reach! ### GMAT/MBA Expert GMAT Instructor Joined 08 Dec 2008 Posted: 13038 messages Followed by: 1251 members Upvotes: 5254 GMAT Score: 770 vikrantr93 wrote: 2 persons start walking on a road that diverge at an angle of 120 degree. if they walk at rate 3 km/h and 2 km/h respectively. Find the distance between them after 4 hours. a. 5 km 2. 4âˆš19 km c. 7 km d. 8âˆš19 km e. None of these Please note that the above solution uses the Cosine Law. You don't need to know this law for the GMAT. In fact, you don't need to know anything about sines, cosines or tangents for the GMAT. My solution requires the addition of some lines and knowledge of 30-60-90 "special" triangles (which is required for the GMAT). Cheers, Brent _________________ Brent Hanneson â€“ Creator of GMATPrepNow.com Use my video course along with Sign up for free Question of the Day emails And check out all of these 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! Senior | Next Rank: 100 Posts Joined 14 Jan 2011 Posted: 35 messages Upvotes: 1 Awesome Brent! your course Rocks!! Master | Next Rank: 500 Posts Joined 21 Aug 2011 Posted: 316 messages Followed by: 6 members Upvotes: 16 Test Date: 24th September Target GMAT Score: 700+ After 4 hours, one has travelled 12 km and the other has 8 kms. Now if we do a little reconstrunction and drop a perpendicular from A on BC extended, we have a right angled triangle, with perpedicular, BC extended and AB as hipotenuse. AB is needed now. length of perpedicular = AC sin 60 = 12sin60 = 6sqrt3 Length of BC extended = 8+ACcos60 = 8 + 4 = 12. Now length of AB = Length of hipotensuse. _________________ If you've liked my post, let me know by pressing the thanks button. • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

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