Question

What is the distance a truck can travel if it moves 7 m/s for 20 seconds?

Answer 1

If it moves 7 m/s and never slows down or speeds up, and it keeps doing this for 20 seconds, then it will cover 7 meters in the 1st second, 7 meters in the 2nd second, 7 meters in the 3rd second, 7 meters in the 4th second, 7 meters in the 5th second, and so on and so forth, twenty times.  All together, it'll cover

7+7+7+7+7+7+7+7+7+7+7+7+7+7+7+7+7+7+7+7 meters

What I did there was:  I wrote down ' 7 ' twenty times.

Now, there's a much easier way to write it.  

In arithmetic, a little dot like this --> · <-- means "times", so we can write

20 · 7  and then we can work it out with our calculator or our pencil.

20 · 7  = 140 meters .

Answer 2

if it moves 7m/s, that means every second it goes 7m.  Now we just multiply by the time (20 seconds) and end up with 140m.