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Question

Sally and Ken drove from Town A to Town B at constant speeds. Ken started his journey 2 hours after Sally. Ken travelled faster than Sally by 40 km/h and overtook her in 3 hours. find Sally’s speed.  

Answer

To the point where overtaking took place,
(i) the ratio of the time taken by —
Sally : Ken
5h : 3h (to the point where overtaking took place)

(ii) the ratio of the speed of —
Sally : Ken
3 : 5

5 – 3 = 2
40/2 = 20
20 x 3 = 60

Ans : 60 km/h.

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5u – 3u = 2u

2u = 40

1u = 20

3u = 60km/h

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Ken travelled 40km more than Sally for each hour.

40 x 3 = 120 (Ken travelled 120km additionally, and thus he overtook Sally)

3 + 2 = 5 (At this time, Sally has travelled for 5 minutes already)

120 / 5 = 24 (It took 5 hours for Sally to be overtaken.)

 

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