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 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.

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