Sure thing! If you want a certain question answered, let me know! This is just the basic things...
Multiplication
So what I do is I first remove the decimal (Say the numbers are 1.24 and 100.9) so it will be 124x1009. After I multiply it, I will count how many numbers are in the decimals, there are a total of three. So that means 125116 would turn into 125.166
If this doesn't help, let me know and I will respond as fast as I can