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Thursday, July 20 2017 @ 07:39 AM CDT
 Forum Index >  Test Paper Related >  Primary 6 Matters
 p6 math speed
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By: tchtby (offline)  Sunday, September 08 2013 @ 11:19 PM CDT (Read 491 times)  
tchtby

A car left Town P for Town Q, at the same time, when a truck left Town Q for Town P,
the average speed of the car was 80km/h while the speed of the truck was 68km/h.
The two vehicles passed each other at a point 24km from the midpoint between Town P and Town Q.
What was the distance between Town P and Town Q?



Can someone please help me solve this question? Thank you.

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By: jo sarah (offline)  Monday, September 09 2013 @ 08:21 AM CDT  
jo sarah

Note: When the vehicles heading towards each other meet,
they would have spent SAME time on their journeys since they started at same time.
So that, ratio of their speeds = ratio of their distances

..|----------------|----------||----------|----------------|
.P...............................M............X................Q......................[ M: midpoint; X: meet]

Speed ratio: 80 : 68 = 20 : 17
Difference in distance = 20u - 17u = 3u ------> 2 x 24 km = 48 km
So that, ................................1u -------> 48 / 3 = 16 km

Distance between P and Q = (20 + 17) x 16 = 592 km

Check: 592/(80+68) = 4 h
In 4 h, car went 320 km and truck went 272, which is 24 from midpoint (592/2)

Cheerio! Big Grin

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