How to Subtract Decimals Math with Mr J

Welcome to Math with Mr. In this video, I'm going to cover how to subtract decimals. Now, if you're able to subtract whole numbers, you're going to be able to subtract decimals. There's just couple of different steps as far as how we set these problems up. Let's jump into our examples and start with number one where we have 29 and 8/10 minus 5 and 73/100. So, the first thing that we want to do, line our decimals up. Meaning, we'll have 29 and 8/10 minus and 73/100. So, the decimals are lined up. That's going to line up all of our places. So, the hundredths, tenths, ones, tens, whatever places you're working with within the problem. The problem does look little off-set. The 5 and 73/100 goes further to the right than the 29 and 8/10. That's okay. The most important part, we have our decimals lined up. Now, we can use placeholder zeros to make this problem look little more lined up. Meaning, we can place zero in the hundredths place right here. We're using placeholder zeros to better align the problem. Remember, zeros to the right of decimal do not change the value. That's an equivalent decimal there. So, we're not changing the value of that number or the problem overall. Now, we're ready to subtract. So, we start with 0 - 3. So, we're going to need to borrow. So, let's borrow from this 8. And now we have 10 - 3, which is 7. Then we move to the tenths where we have 7 - 7, which is 0. Now, bring our decimal straight down. The decimal should be lined up throughout the entire problem, even in the answer. So, we place the decimal in our answer by bringing it straight down. Then we move to the ones where we have 9 - 5, which is 4. And then lastly, the tens place we have 2 - 0. We don't have anything in the tens place for 5 and 73/100. So, let's just bring that two down. And our final answer is 24 and 7/100. Now, before moving to number two, do want to mention couple of common mistakes when we subtract decimals. The first one being, let me rewrite the problem here. 29 and 8/10 minus 5 and 73/100. So, the first mistake would be dropping this three here, assuming that we can just drop the three. But in reality, remember we have zero here and we need to borrow. So, don't just drop number if there is nothing above it. We need to use borrowing because there is zero there. The other mistake would be lining the problem up like this. So, lining up the digits instead of lining up the decimals. So, in the case of this right here, you can see that the decimals are lined up. We have three digits above three digits. Remember, line the decimals up. So, this will not give correct answer. Let's move on to number two and try another example. So, we have 168 and 9/100 minus and 452 thousandths. Let's use placeholder zero so everything goes over to the thousandths place. And now we're ready to subtract. Don't drop that two because we have 0 - 2 there and we need to borrow. So, let's borrow from the nine. And now we have 10 - 2, which is 8. So, an eight in the thousandths. Then we move to the hundredths. So, 8 - 5, which is three. Now, for the tenths. So, we have 0 - 4, we're going to need to borrow. 10 - 4 is 6. Remember, bring your decimal straight down. It should be lined up throughout the entire problem when we subtract decimals. Then we move to the ones. So, 7 - 1 is 6. Then the tens. So, 6 - 3 is 3. And then finally, the hundreds where we have 1 - 0 there. So, we can just drop the one. And we have an answer of 136 and 638/1000. So, there you have it. There's how you subtract decimals. hope that helped. Thanks so much for watching. Until next time. Peace.