Question 859073
Let j = the mass of the jug in grams.

Difference between 1/5 full and 4/5 full is |560-740| grams.
That is 3/5 of capacity is 180 grams.  Proportioned to full 5/5 of capacity, {{{(5/3)180=300}}} grams.


Taking either of the given quantities, here trying 1/5 full, {{{j+(1/5)300=560}}}; solve this for j.