Learn about Addition of Decimals This lesson deals with addition of decimals. Let’s try both these problems one by one. The first one wants us to add three of these decimals together which are 0.38 added with 0.727+0.45. So when we are adding decimals, there are a couple of rules that we need to remember. Rule A is that all the decimals that we’re adding should have the equal number of digits after the decimal point. Here we see it’s got two digits after the decimal point. This number has three, and this one has two. So, all should ideally have equal number of digits after the decimal point. If not, we can convert them, so they do. So 0.38 instead of this, we can write a 0.380. It makes no difference because after the decimal point, if we’ve got an ending 0, it adds no value. 0.727 has already got three spaces, three decimal spots, and this I can change to 0.450. So we need to make sure all of them have equal number of digits after the decimal point. The second is we can add but before we do, we need to align them with the decimal spots. So let me write this another way 0.380, 0.727 and 0.450.We will align them so the decimal spots are absolutely aligned, and we will just add them like regular numbers. So 0, 7, 0 adds to 7. 8+2=10, 15, 5, 1gets carried over, 4+7=11+both 15, 5. 1gets carried over and 1. So the end result is, 1.557 which is what we’re looking for. Let’s try the second one with the red color. The second one says, -5.78 added to -18.3. Now key to remember, I'm going to take some extra space. Is if both the numbers have the same sign, then it’s an addition operation. If both numbers have the same sign, then it’s an addition operation. So we can write -5.78 add it to -18.3. Well -18.3 has got only one decimal up to the point, so we’ll make it -18.30. It’s aligned. 8 and 0 is 8, 7+3 is 10, 0 with 1 carried. 5+1 is 6, +8=14, with 1 carry 1, and 1 as 2. 24.08, but both of them are negative so maintain that. So -5.78 add it to -18.3 is -24.08.