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To travel 720 km, a Express train takes 6 hours more than Duronto. If however, the speed of the Express train is doubled, it takes 2 hours less than Duronto. The speed of Duronto (in km/hr) is?
- A60
- B72
- C66
- D78
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CCommunity
Let the speed of Duronto be ‘x’ km/hr
Time taken by Duronto to travel 720 km = 720/x hrs.
Let the initial speed of Express train be ‘y’ km/hr
Time taken by Express train to travel 720 km = 720/y hrs.
? Express train takes 6 hours more than Duronto,
⇒ 720/y = 6 + 720/x ----(1)
When the speed of Express train is doubled, it takes 2 hours less than Duronto,
⇒ 720/2y = 720/x – 2
⇒ 720/y = 1440/x – 4
Substituting from (1),
⇒ 6 + 720/x = 1440/x – 4
⇒ 6 + 4 = 1440/x – 720/x
⇒ 10 = 720/x
⇒ x = 720/10 = 72 km/hr
∴ Speed of Duronto = 72 km/hr
Time taken by Duronto to travel 720 km = 720/x hrs.
Let the initial speed of Express train be ‘y’ km/hr
Time taken by Express train to travel 720 km = 720/y hrs.
? Express train takes 6 hours more than Duronto,
⇒ 720/y = 6 + 720/x ----(1)
When the speed of Express train is doubled, it takes 2 hours less than Duronto,
⇒ 720/2y = 720/x – 2
⇒ 720/y = 1440/x – 4
Substituting from (1),
⇒ 6 + 720/x = 1440/x – 4
⇒ 6 + 4 = 1440/x – 720/x
⇒ 10 = 720/x
⇒ x = 720/10 = 72 km/hr
∴ Speed of Duronto = 72 km/hr