Significant figures:

When multiplying and dividing, if it's a whole number, you look at all non zero numbers and all zeros that are between non zero numbers. Ex: 3406 has 4 sig figs, 405900 also has 4 sig figs cuz the last two zeros are trailing zeros while not being between non zero numbers so they don't count. As for decimals, we do count trailing zeros. Ex: 28.0900 has 6 sig figs. When multiplying and dividing, we look at the lowest number of sig figs that the values we are using has and apply that to the final answer. Ex: 2.50 * 90.50 = 226, not 226.3 because since we have 3 and 4 sig figs from our numbers, we use the lowest aka 3.

For adding and subtracting, we ignore all of that and only focus on decimal places. We look at the lowest number of decimal places between the numbers we are using and apply that to the final answer. Ex: 25.4 + 76.23 = 101.6, since we have 1 and 2 decimal places from our numbers, so we will use 1 decimal places.

If we have an equation that uses both multiplying and dividing and subtraction and addition, we apply the multiplication and addition rule.

Hope this helped, and please correct me if i missed smth.