+0

Average speed

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The distance between town P and town Q is 180km. A drives at an average speed of 60km/h from town P to town Q while B drives from town Q to town P at an average speed of 48km/h. Assuming that they start their journey at 8am, when do they meet each other?

Guest Aug 5, 2017
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#1
0

Average speed = Distance travelled / Time

Let the distance travelled by A = D, then we have:

Distance travelled by B = 180 - D. But we have:

D/60 = (180 - D)/48, solve for D

D = 100 km - distance travelled by A

180 - 100 =80 km - distance travelled by B

100/60 =1 2/3 hours, or they will meet after 1 hour and 40 minutes, or at 9:40 am

Guest Aug 5, 2017
#2
+79894
+1

Note that   Distance / Rate  =  Time

Since they travel the same time......let the distance that A drives  = D

And let the distance that B drives  = 180 - D

So....equating times [ in hours ], we have that

D / 60  =  [ 180 - D ] / 48    cross-multiply

48D  = 60 [ 180 - D ]     simplify

48D  = 10800 - 60D      add 60D to both sides

108D  =  10800       divide both sides by 108

100 = D  ....so ...the time they meet  =  [D / 60 ]  hrs.  =  [ 100/ 60 ]  hrs.  =  [5/3]  hrs   =

[5/3] * 60 minutes =   100 minutes after 8AM  =  9:40 AM

CPhill  Aug 5, 2017
edited by CPhill  Aug 5, 2017

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