This works exactly like regular addition...  you just line up the decimal points!

3.21 + 4.5 = 7.71

Here's another one:

5.649 + 39.27 = 44.919

See?  It's pretty easy!

So, what about adding a whole number and a decimal?  No problem!

528 + 7.49 = 535.49

It's a snap!