Puzzle:

A fly is flying between two trains, each travelling towards each other on the same track at 60 km/h. The fly reaches one engine, reverses itself immediately, and flies back to the other engine, repeating the process each time. The fly is flying at 90 km/h. If the fly flies 180 km before the trains meet, how far apart were the trains initially?

Solution:

Initially, the trains were 240 km apart.

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Solution:

Initially, the trains were 240 km apart.

The fly is flying at the speed of 90 km/h and covers 180 km. Hence, the fly flies for 2 hours after trains started. It's obvious that trains met 2 hours after they started travelling towards each other. Also, trains were travelling at the speed of 60 km/h. So, each train traveled 120 km before they met. Hence, the trains were 240 km apart initially.

## 6 comments:

240 kms....................rajesh

240 KM

Relative Velocity between trains

Vr = Vt1 + Vt2 = 120km/h

Given Vf = 90km/h

Distance travelled by fly Sf = 180km/h

Sf = Vf * Tf

--> tf = 180/90 = 2 hrs;

So fly flew for 2 hrs.,

since at Tf 2 trians met each other

St = Vr * tf

St = 120 * 2 = 240 Km

so, trains are initially separated by 240 km

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