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## Explanation

A train 800 meter long is running at a speed of 78 km/h. If it crosses a tunnel in one minute, then the length of the tunnel will be determined according to the formula mentioned here under as;

Length = speed x time ________ (i)

Assuming the length of the tunnel = n

Total length = n + 800

Speed will be converted to m/sec and time is also given (1 min = 60 sec).

By substituting all the value in the equation (i); length = 500 meter

## To Find

Length of the tunnel = ?

## Solution

Given speed = 78 km/h

Speed in m/sec = (78 x 1000)/3600

Speed in m/sec = 195/9 m/sec

Time required to pass the tunnel = 1 min = 60 sec

Let suppose

the length of tunnel = n

so, total length = n + 800

Now,

length = speed x time

n + 800 = (195 x 60)/9

n + 800 = 11,700/9

n = 1300 – 800

**n = 500 meter answer**

### Conclusion

A train 800 meter long is running at a speed of 78 km/h. If it crosses a tunnel in one minute, then the length of the tunnel will be **500 meter**.