Math word problem

 What I know 

1000m = 1km

The train is 1000m long

The tunnel is 3000m long

30 seconds pass since the last car had entered the tunnel until the time the front of the engine emerges from the other end

Determine the speed of the train in kilometres per hour

Solution

The train is 1000m long and the tunnel is 3000m long so you need to subtract  3000m - 1000m = 2000m

30 seconds passed since the last car entered the tunnel so 2000 divided by 30 = 66.7m per second is how fast the train traveled in one second

1 minute has 60 seconds so 66.7 x 60 = 4002m per minute 

1 hour has 60 minutes so you need to multiply by 60 again 4002 x 60 = 240, 120 m per hour

240,120 divided by 1000 =  240.12km

The tran travels 240.12km in one hour