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Mr Tan drove from Town A to Town B at a constant speed of 40 km/h. He then drove back from Town B to Town A at a constant speed of 70 km/h. The total time taken for the whole journey was 5.5 h. Find the distance between the two towns.

 Jun 2, 2020
 #1
avatar+21826 
+1

Let  T  represent the time going from A to B.

 

The distance =  rate x time   --->   distance  =  40·T

 

Since the total time was 5.5 hrs, the time returning from B to A was  5.5 - T  hours.

 

The distance returning  --->   distance  =  70·(5.5 - T)

 

Since the distance going is the distance returning:  40·T  =  70·(5.5 - T)

Solving:                                                                      40T  =  385 - 70T

                                                                                 110T  =  385

                                                                                       T  =  3.5 hours

 

The distance going     =  40·3.5  =  140 km

The distance returning  =  70·2  =  140 km

 Jun 2, 2020
 #2
avatar+25776 
+1

d = distance           r = rate      d/r = time

 

d/40  +    d /70   =  5.5

110d = 5.5 *70*40

d= 140 km

 Jun 2, 2020

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