How to divide/multiply a cell value without leaving the cell

So, part of the problem is adequately describing what I want in a sentence. I wasn't able to find anything like it in my search.

What I want is a short-hand for the following:

I want to change the value of a cell by the product/quotient (or any other operator) of an integer (or decimal). I have a range of cells with numerical values. Each has more than two decimal places and I want to capture all of the decimals in the conversion. In this case, I want to divide each cell in the range by 2, replacing each cell with this result.

How I know to do it is to create a new column with a formula that references the original and divides it by 2. (B1 = 12.5. New cell C1 set to = B1 /2 (=6.25)). Then, I copy the new cell, C1, and paste the formula results back into the original, B1.

I feel like there is (should be) a shorthand for this where I can just change the value in a cell by an operator and a constant without having to exit the cell and save some steps. Any chance?? Thank you