Sig fig substraction help!? chem?

WARNING: the rule for add/subtract are different from multiply/divide. A very common student error is to swap the two sets of rules.
Another common error is to use just one rule for both types of operations

For addition and subtraction, look at the decimal portion (i.e., to the right of the decimal point) of the numbers ONLY.
Here is what to do:
1) Count the number of significant figures in the DECIMAL portion of each number in the problem.
(The digits to the left of the decimal place are not used to determine the number of decimal places in the final answer.)
2) Add or subtract in the normal fashion.
3) Round the answer to the LEAST number of places in the decimal portion of any number in the problem.
In you problem:
80 has no figures in the decimal portion of the number
2.99 has 2 figures in the decimal portion of the number
Therefore the answer must have no figures in the decimal portion of the number
Conventionally: 80 - 2.99 = 77.01
To correct number of significant figures: Answer = 77

80 is correct to whole number.
2.99 is correct to 2 decimal number.

For addition and subtraction, the answer should be correct to the lowest precision, i.e. to the whole number.
Hence, 80 - 2.99 = 77 (to the whole number)
In other words, the answer to correct to 2 significant figures.

Sig fig substraction What kind of help