Explanation:
by bringing all terms to the same fractions (with the same denominator).
so, we have
7
5/7
that means we want to bring both numbers to .../7 form.
7 means 7 whole units.
1 whole unit has now many parts ?
if we aim for 2 parts, that makes 1 whole unit 2/2.
if we aim for 3 parts, 1 whole unit is 3/3.
...
you see, 3/3 = 1/1 = 1.
that is the whole trick.
so, we are looking for 7 parts, and 1 whole unit is 7/7.
now we have 7 whole units.
how many parts are those ?
well, 7 × 7/7 = 49/7
there we go.
we have
7 - 5/7 = 49/7 - 5/7 = 44/7 = 42/7 + 2/7 = 6 2/7