Explanation:
x = Moe's money
y = Loki's money
z = Nick's money
1/5 x = 1/4 y = 1/3 z (Moe gave 1/5, Loki 1/4, Nick 1/3, but all donations to Ott are the same amount of money).
that also means
y = 4/5 x
z = 3/5 x
in total the group has
x + 4/5 x + 3/5 x = 5/5 x + 4/5 x + 3/5 x = 12/5 x
Ott got 3× 1/5 x (since everybody gave the same amount of money, so it is in sum 3 times of what Moe gave).
so, Ott now has 3/5 x , out of a total of 12/5 x.
his fractional part is therefore
3/5 / 12/5 = 3/5 × 5/12 = 3/12 = 1/4.
he has 1/4 of the group's total money.