Adding and Subtracting Decimals in Word Problems

Adding and Subtracting Decimals in Word Problems

Adding and Subtracting Decimals in Word Problems

The key with adding and subtracting decimals is just to line them up. So let’s look at an example. Margaret is mailing 3 letters that weigh 3 and 7 tenths ounces, 2 and 913 thousandths ounces, and 2 an 82 hundredths ounces.

What is the combined weight of the letters? This word combined is key, because it tells us we need to add those 3 values together, and once we know that we’re adding, we can just line them up and add them together. 3 and 7 tenths ounces, 2 and 913 thousandths ounces, and 2 and 82 hundredths ounces.

Okay, so this looks kind of weird because you’re used to lining things up on the right side, especially when you’re adding whole numbers, not decimals. What you can do is you can add 0s behind these numbers, behind the decimals at the end of your numbers, and it kind of rounds them out and makes them look a little less weird, because when you add 0s to the end you’re not changing the value of the number.

Think about this like if it was money. If you have 3 dollars and 70 cents, it’s still 70 cents if you add a 0, and it’s still 70 cents if you add another 0, and so on, and so forth. That’s why we can add those 0s there. Ok, now we just need to add this first column we get 3, and 3 again.

Here we have 9 plus 7 is 16, plus 8 is 24, carry your 2. Make sure you don’t forget that decimal in your answer, it’s just lined up with all the other decimals. Then 2, 4, 6, 9, so, it’s 9 and 433 thousandths ounces. Subtraction works the same way, we can do a real quick subtraction problem.

I’ll just give you the word problem out loud. Let’s say we had 5 dollars and 76 cents, and we spent 2 dollars, and then you might be asked, how much is left? I know this is a really oversimplified question, but again, the point is just line up your decimals. In this 2 dollars (in that number there) you don’t actually see a decimal, well, the decimal, and any number (if you don’t see one) is at the end of the numbers.

You could put the decimal here. If you spent 2 dollars and you want to know what’s left, spent tells you to subtract. You have 5 and 76 hundredths minus 2, and you could add those 0s, because again, adding those 0s after a decimal doesn’t change the value.

Then you could subtract. You have 6, 7, 5 minus 2 is 3, so you would have 3 dollars and 76 cents left. There’s an example of how to add and subtract decimals when they’re in a word problem. Just line them up.

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by Mometrix Test Preparation | Last Updated: April 23, 2019