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Lesson 2: Subtracting decimals (tenths)

# Strategies for subtracting more complex decimals with tenths

Learn all about subtraction of decimals, particularly those in the tenths place. The focus is on various strategies like decomposing whole numbers into tenths and using a number line for visualization.

## Want to join the conversation?

• If want you to subtract 3-1.5 don't you add two zero's to the 3 then add a decimal between 3 and the two zero's? Or is there another way to do it instead of doing that?(adding the two zero's and adding the decimal between the 3 and the zero's)
• Since .5 has only one digit, you only need to add a single zero, 3.0. Or break into parts, (3 - 1) - 1/2 = 2 - 1/2 = 1 1/2.
• why do we line up decimal points when adding and subtracting?
• We line up decimal points and stuff a lot because then we have a critically low chance of mixing up places, like thinking the tenths are in the hundredth, getting the whole thing wrong, and having to restart frustrated. Sorry no one answered you for a long time.
• Why did he say 1 and 0 tenths is 0 and 10 tenths?
• 1 and 0 tenths is the same as 0 and 10 tenths
• at why does he add the 0.5?
• He broke 4.5 down into 4 + .5 and -2.8 into -2 - .8.
• I just made 2 into 2.0 and it was easier to solve it
• I know that division of decimals is not in this video, but just how do you divide decimals, say 0.58 divided by 0.12?
• Put it over the place value then do crisscrossed multication.

Me: do 10 - 2 and and a period in front of your anwser and boom your done with the first question.
• I feel tired. Don't you?
• OMG when I think about it yes! yes, I do .
(1 vote)
• Another clear way to say 2 - 1.2 is putting down 20 - 12 which gives you 8.
• I'm confused about 4.5-2.8, wouldn't it be 2.3? why was the 1+1 added?
• No, the answer is 1.7. Sal was breaking down the problem into smaller and, arguably, easier steps.

1. Convert: 4.5 - 2.8 = 4.5 - (2.5 + 0.3)
2. Use the Distributive Property: 4.5 - (2.5 + 0.3) = 4.5 - 2.5 - 0.3
3. Use the Associative Property: 4.5 - 2.5 - 0.3 = (4.5 - 2.5) - 0.3
4. Subtract: 4.5 - 2.5 = 2
5. Replace the result of 4 in the converted equation: 2 - 0.3
6. Convert: 2 - 0.3 = (1 + 1) - 0.3
7. Use the Associative Property: (1 + 1) - 0.3 = 1 + (1 - 0.3)
8. Subtract: 1 - 0.3 = 0.7
9. Replace the result of 8 in the converted equation: 1 + 0.7
10. Add: 1 + 0.7 = 1.7

As you can see, in step 6, the 2 was converted into 1 + 1. This is allowed because 1 + 1 is equal to 2.

Mathematical manipulations like this will become increasingly common the further you go into math. The idea is to make solving an equation easier, and you can change it however you want as long as those changes don't fundamentally change the result.

So, converting 2 - 0.3 into 1 + 1 - 0.2 is okay, but converting 2 - 0.3 into 2 - 0.3 + 0.3 would not be because it changes the answer.
(1 vote)