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total distance ——- 7u

2u ——- 18 x 5 = 90

1u ——- 90/2 = 45

7u ——- 7 x 45 = 315

John’s speed ——- 315/5 = 63

David’s speed ——- 63 – 18 = 45

90/45 = 2

Ans : 2h.

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hi Alfretztay, thanks.

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Hi ATM 82517, welcome .

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I thought the question is strange. David travelled 5/7 of distance in 5 hours so he would need another 2 hours to travel remaining 2/7 of distance (by proportion). 

The question may have a 2nd part asking for something tougher like to calculate speed. You may want to check again. 

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hi sahmom, thanks 

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The 18 km/h is a distraction.

 

In 5 hour, David covered 5/7 of the distance.

5/7 -> 5 hour

1/7 -> 5 ÷ 5 = 1 hour

To cover the remaining 2/7, he would need 2 × 1 = 2 hours

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hi  bigdevil, thank you ur explanation. 

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