Another applet illustrates the same idea. Drag the mouse slowly and watch equal fractions light up. Bearing in mind the u-property reduces addition and subtraction of fractions to that of integers. Do not add apples and oranges. Whether or not the result is in lowest terms is absolutely irrelevant at this point.
Division is of course the last operation to discuss.
In my view, division of fractions is best explained in terms of the u-property. 12 tarts divided by 3 tarts gives 4. This is again convenient to tackle quantities expressed in the same units. Alexander Bogomolny 2789751 .