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 Algebra Pre-Algebra and Basic Algebra Math Forum

 March 11th, 2008, 05:21 AM #1 Newbie   Joined: Mar 2008 Posts: 1 Thanks: 0 Distance, time and rate To cover the distance of 180 km, with average speed 15 km/h less than expected, took 1 hour longer than expected. Find the average speed. March 11th, 2008, 06:28 AM #2 Senior Member   Joined: May 2007 Posts: 402 Thanks: 0 If v is the average speed, then the time to cover 180km takes: t=180/v Now, you say that if we were going with a speed that's 15 km/h smaller than the average, we would cover the same distance in 1 hour more. So, we have: 180/(v-15) = 180/v+1 180 v/(v-15) = 180+v 180 v = 180(v-15)+v(v-15) 180 v = 180 v-15*180+v(v-15) 0= v^2-15v+15*180 Using the quadratic formula, we get: v1=-45 v2=60 Since the first answer makes no sense, the answer is v=60. Checking: 180/(v-15) = 180/v+1 180/(60-15) = 180/60+1 180/(60-15) = 3+1 4=4 March 11th, 2008, 12:09 PM #3 Global Moderator   Joined: Dec 2006 Posts: 21,026 Thanks: 2257 No. The average speed was expected to be 60 km/h, but was actually 45 km/h. Tags distance, rate, time Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post HellBunny Algebra 3 August 16th, 2012 12:46 PM Mighty Mouse Jr Algebra 4 July 9th, 2010 06:47 PM Mighty Mouse Jr Algebra 3 July 9th, 2010 03:42 PM Mighty Mouse Jr Algebra 4 June 29th, 2010 03:24 PM marie789 Algebra 2 December 11th, 2007 08:13 PM

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