The weight of the hamburger is 160g after two bites.
Each bite takes away 20% of the weight of the burger, so we'll divide the initial weight by a percentage to find the weight before the bite.
The starting weight is 160g. Because 20% of the weight was removed from a bite, we'll divide this weight by the percentage of the burger remaining after the bite:

80% of the burger is left after a bite. Convert this fraction into a decimal by dividing by 100:

Divide the initial weight by this decimal:

The weight of the burger before the second bite was 200.
We'll do the same procedure for the first bite. The initial weight is 200, and there is 80% of the burger remaining after the first bite. Because 80% is 0.8 in decimal form, divide 200 by 0.8:

The starting weight of the burger before the bites was
250 grams.