You can use Paste Special to do maths!
Say you have a list of numbers, and for some reason you want to divide them all by 100. You could write a formula to do that, you could type a few answers and use flash fill, or you can use Paste Special.
Type 100 into a cell. Copy that cell. Select all the numbers you want to divide by 100. Right click (or use Shift + F10) and choose Paste Special, then in the Operation area choose Divide.
As you can see, you could also choose, Add, Multiply or Subtract.