After traveling 35km, a train meets with an accident and travels at (3/4)^th of the usual Speed and reaches 45 min late. Had the accident happened 15km further on it would have reached 30 min late. Find the usual Speed?

সঠিক উত্তর

20 km/h

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Question: After traveling 35km, a train meets with an accident and travels at (3/4)th of the usual Speed and reaches 45 min late. Had the accident happened 15km further on it would have reached 30 min late. Find the usual Speed?

Solution:
Here there are 2 cases
Case 1: accident happens at 35 km
Case 2: accident happens at 50 km
Difference between two cases is only for the 15 kms between 35 and 50.
Time difference of 15 minutes is only due to these 15 kms.

In case 1, 15 kms between 35 and 50 is covered at (3/4)th Speed.
In case 2, 15 kms between 35 and 50 is covered at usual Speed.

So the usual Time 't' taken to cover 15 kms, can be found out as below.
(4/3)t - t = 15 mins [s = vt]
⇒ t = 45 mins, d = 15kms

so usual
Speed = Distance/Time
= 15/45min
= 15/(3/4) km/hr.
= 20 km/hr.

সকল অপশন

রেফারেন্স মাত্র

20 km/h সঠিক

10 km/h

30 km/h

35 km/h

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