About this video
Sal calculates 10.1 - 3.93. He lines up the decimal points, writes 10.1 as 10.10, then regroups across several places (tens to ones, ones to tenths, tenths to hundredths) before subtracting to get 6.17.
You'll be able to
- line up place values and add a zero so both numbers have the same decimal places.
- regroup across more than one place when subtracting decimals.
- subtract decimals to the hundredths place.
Key words
- place value
- The value of a digit based on where it is, like ones, tenths or hundredths.
- regroup
- Trade one unit in a place for 10 units in the next smaller place.
- hundredths
- The second place after the decimal point; 10 hundredths make 1 tenth.
Transcript
Let's try to calculate 10.1 minus 3.93. And I encourage you to pause this video and try it on your own first, and then we can think about whether we did it the same way. So let's just rewrite it, aligning the decimal and the different place values. So 10.1 minus-- the 3 is in the ones place, so I'll put it right under the 0-- 3.93.
Now, let's just try to calculate this. Now, before we subtract, we want all the numbers on top to be larger than the numbers on the bottom. And we don't even have a number here. We could stick a 0 here. Let me do that in a different color here. We could stick a 0 here.
10.1 is the same thing as 10.10, but we still face an issue here. 0 is less than 3. 1 is less than 9. 0 is less than 3. So we're going to do a little bit of regrouping. So let's do that regrouping. So we could take a 10 away, one 10 away, and then one 10 is the same thing as 10 ones.
So I could write a 10 in the ones place. And I could take one of those ones away so I'm going to have nine ones, and give that one to the tenths place. Well, one is 10 tenths. 10 tenths plus 1 tenth is going to be 11 tenths. Now, I could take one of those tenths away and give it to the hundredths place.
1 tenth is 10 hundredths. And now I have a higher digit in the numerator, or at least as equal in the numerator as I have in the denominator. So 10 minus 3 is 7. 10 minus 9 is 1. I have the decimal. 9 minus 3 is 6. And then I have nothing over here. So 10.1 minus 3.93, 6.17.
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