1, basic formula:

Distance = speed × time

Speed = distance/time

Time = distance/speed

2. Follow-up questions:

Catch-up time = distance difference/speed difference

Speed difference = catching distance/catching time

Catch-up distance = speed difference× catch-up time

3, running water problem:

Downstream stroke = (ship speed+water speed) × downstream time

Upstream stroke = (ship speed-water speed) × upstream time

Downstream speed = ship speed+current speed = ship speed-current speed.

Still water velocity = (downstream velocity+upstream velocity) ÷2

Water velocity = (downstream velocity-upstream velocity) ÷2

4. Formula of inverse stroke problem:

Speed and time of meeting (leaving) = distance of meeting (leaving)

Pick-up (departure) distance ÷ (speed sum) = pick-up (departure) time.

Meet (leave) distance ÷ meet (leave) time = speed and.

5. The train bridge formula:

(bridge length+conductor length) ÷ speed = crossing time

(Bridge length+conductor length) ÷ Crossing time = speed

Speed × crossing time = sum of bridge length+vehicle length