a whole or 1, is when the numerator and denominator are the same, namely 2/2, 3/3, 10000/10000 is a whole.
on Saturday they travelled 5/8 of the way, now, the whole being 8/8, so if we take 5/8 from 8/8, we're simply left with 3/8, that's the remaining distance to grandmas house.
on Sunday they travelled 1/3 of that remaining amount, how much is that? well, is simply their product,
[tex]\bf \cfrac{3}{8}\cdot \cfrac{1}{3}\implies \cfrac{3}{3}\cdot \cfrac{1}{8}\implies \cfrac{1}{8}[/tex]
