If 12.30 g and 0.2 g are added, how many decimals?

The sum is reported with one decimal place, so the result is twelve point four grams.

When you add twelve point three zero grams and zero point two grams, first do the normal addition: twelve point five zero grams. But because the rule is to match decimal places, not significant figures, you look at how many digits are after the decimal in each measurement; twelve point three zero has two decimal places and zero point two has one decimal place, so you must round the result to one decimal place, giving twelve point four grams. Think of decimal places like how many steps you count after the dot, and you always use the fewest number of those steps when adding or subtracting. This keeps your answer honest about how precise the measurements really are.

A common mistake is trying to use significant figures instead of decimal places for addition and subtraction, which can give the wrong rounded result, so remember to use decimal places for these operations. Another error is forgetting to line up the decimal points before adding, and that can make the digits add in the wrong columns, so always write numbers vertically with the decimal points aligned before summing. Some students also round too early during intermediate steps, and that can change the final answer, so keep extra digits until the end and then round to the correct number of decimal places.

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How to Add 12.30 g and 0.2 g

1. Add numbers normally first
2. Use decimal places rule
3. Count digits after decimal point
4. Use fewest decimal places
5. Line up decimals when adding

Common Addition Mistakes with Decimals

1. Using significant figures instead of decimal places
2. Not aligning decimal points before adding
3. Rounding too early during calculations

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