SOLUTION: A train X leaves Meerut at 5a.m and reaches Delhi at 9a.m. Another train Y leaves Delhi at 7a.m and reaches Meerut at 10:30a.m . At what time do the two trains cross one another?
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Question 825045: A train X leaves Meerut at 5a.m and reaches Delhi at 9a.m. Another train Y leaves Delhi at 7a.m and reaches Meerut at 10:30a.m . At what time do the two trains cross one another? Answer by Edwin McCravy(20060) (Show Source):
You can put this solution on YOUR website! A train X leaves Meerut at 5a.m and reaches Delhi at 9a.m. Another train Y leaves Delhi at 7a.m and reaches Meerut at 10:30a.m . At what time do the two trains cross one another?
Suppose it is N km from Meerut to Delhi
Train X travels N km in 4 hours, so X's speed is N/4 km/hr
Train Y travels N km in or hours, so Y's speed
is N÷ = N× = 2N/7 km/hr
Let t = the time after 7a.m. that train Y travels
Then, t+2 = the time after 5a.m. that train X travels
| speed × time = distance
-------------------------------------
train X | N/4 | t+2 | (N/4)(t+2)
train Y | 2N/7 | t | 2Nt/7
Equation:
Train X's distance + Train Y's distance = N km
(t+2) + = N
Multiply by LCM = 28
7N(t+2) + 8Nt = 28N
Divide by N
7(t+2) + 8t = 28
7t + 14 + 8t = 28
15t + 14 = 28
15t = 14
t = 14/15 hr = (14/15)×60 = 56 min.
56 minutes after 7a.m. is 7:56a.m.
Edwin
[It is only 88 km from Meerut to Delhi, so both trains are very slow! :) ]
