Alpha And Charlie Can Finish A Work In 15 Days, Beta In 5 Days. Beta And Charlie Start The Work But Are Forced To Leave After 3 Days. The Remaining Work Was Done By Alpha In:

[Rossini18]

A Delhi express train passes over a 264m long tunnel in 20 seconds and crosses a railroad in 8 seconds. Calculate the speed of the train?

[jno]

13.2 metres per second. But why would a train cross a railroad rather than going along it?

[davebro]

Qu 1. - Can't solve depends how fast Alpha works.

Qu 2. - 79.2 km/h

[JJ109]

The length of the train takes 8 seconds to pass any point.
Therefore the tunnel takes 20 - 8 = 12 seconds

Q 2 = 264/12 = 22 meters per second
= 22 * 2600 metres per hour
= 79200 metres per hour
= 79.2 kph
(agree with davebro!)

[JJ109]

^^22 * 3600!!!!

[JJ109]

Assuming Alpha takes 15 days to complete the work by "himself"
Same for Charlie

After 3 days Beta alone has completed 3/5
Charlie has completed 3/15 = 1/5
Therefore after 3 days 3/5 + 1/5 = 4/5 has already been completed

This leaves 1/5 of the work to be completed by Alpha
15 /5 = 3 days