That's goofy, given that the lines were at different scales. Besides, as someone else pointed out, people on the metric system don't use fractions for meter. They use a decimal number.
Yes. That was the second part of the lesson. They were taught to methods for working the problems, then had to work some problems with a number line and others by finding a common denominator and comparing.
Anybody can find a common denominator, but it's more convenient to find the least common denominator. Are they teaching the kids how to do that?
Yes.