Adding and Subtracting Decimals How to Math with Mr J

Welcome to adding and subtracting decimals with Mr. In this video, we're going to be discussing how to add and subtract decimals and the steps we need to take in order to successfully do so. On your screen, you see four problems, two addition and two subtraction. We're going to work through these four together and if at any point you want to try couple on your own, feel free to press pause, solve the remaining problems or whichever problems you want to solve, press play when you're ready and check your work with mine. At the top of your screen in blue, you see the steps to adding and subtracting decimals. So, keep those in mind as we work through. So, let's jump right in to number one. So, for number one, we have 45 and 6/10 plus 3 and 89/100. So, our first step, we need to set the problem up, rewrite it vertically or up and down and we need to line up the decimals. So, we'll write out 45 and 6/10 plus 3 and 89/100. The decimals are lined up, therefore all the places are lined up. Now, we can insert placeholder zeros if need be. So, take look at the nine. It's kind of hanging off to the right. The 3 and 89/100 goes to the hundredths place. So, we want the 45 and 6/10 to go to the hundredths place, too. That way we have something above the nine there and it lines up little better. You can add zeros to the right of decimal and it does not change the value of that number. So, again, you can use placeholder zeros to the right of decimal and it doesn't change the value. This only works for decimals though. You can't add zeros to the right of whole numbers or else it does change the value. So, use placeholder zeros and then we can add or subtract. So, 0 + 9 is 9. 6 + 8 is 14. Carry the one. Bring your decimal straight down. It should be lined up throughout the whole problem. 1 + 5 is 6 + 3 is 9 and then four. So, 49 and 49/100. Number two, we have 15 + 4 and 88/100. So, for whole number, we put the decimal right after it. Now, we can line up 4 and 88/100. And this is addition. So, here the problem's offset like number one, we had to use placeholder zeros. So, for the 15, we could put zero in the tenths and zero in the hundredths. Now, we're all lined up and ready to add. 0 + 8 is 8. 0 + 8 is 8. Bring the decimal straight down. 5 + 4 is 9. 1 + 0 there is 19. Or I'm sorry, you have the one there, which gives us 19. So, 19 and 88/100. So, number three, we have subtraction, which it's the exact same rules except when you get to this third step over here, you subtract. So, let's write out our problem, lining up the decimals. And it's subtraction. So, let's put the placeholder zero there. And now it's time to subtract. So, we cannot do 0 - 7, so we need to borrow. So, now we have 10 - 7, which is 3. Cannot do 5 - 6, so we need to borrow. So, we get to 15 - 6, which is 9. Bring the decimal straight down. So, we need to borrow again. We can't do 4 - 9, so we need to borrow from the three or the tenths place here. And we get 14 - 9, which is 5. And then we have the two. So, 25 and 93/100. Line up the decimals, use placeholder zeros, add or subtract. So, just like number two here, we have whole number in number four. So, the 23 and we put the decimal right after. Then we have eight and 8/10. And subtract. So, let's put the placeholder zero and we are ready to solve. So, we can't do 0 - 8. Don't just drop the eight there. We need to borrow. 10 - 8 is 2. Decimal straight down and we need to borrow again. So, 12 - 8 is 4. And then we have the one. So, 14 and 2/10. So, that's adding and subtracting decimals for you and the rules or steps we need to take in order to get to the correct answer. So, make sure you line up your decimals, use placeholder zeros, and then add or subtract. Thanks so much for watching. Until next time, peace.