unit fractions are those where the denominator is one, so the easiest way to write 4/5 as as sum of unit fractions is by adding 1/5 four times:
1/5 + 1/5 + 1/5 + 1/5 = 4/5
that is because as the fractions share the same denominator (lower part), we only have to add the numerators (upper part)
