You shine a light in a dark tunnel towards your friend the distance between the two of you are 25m how long does it take for the light to cover this distance

0.000000083333 seconds = 83.333 nanoseconds

Explanation:

The speed of light is approximately 300.000.000 m/s, that means in one second, the light travels 300.000.000 meters.

We can solve that problem using rule of three:

If the light travels 300.000.000 meters in 1 second, to travel 25 meters how long it will take? (let's call the time we want by "T")

300.000.000 - 1

25 - T

300.000.000/25 = 1/T

T = 25/300.000.000

T = 0.000000083333 seconds = 83.333 nanoseconds