Excel: How to keep some cells blank

I have an Excel spreadsheet to which I am adding data on an almost dai开发者_运维知识库ly basis. It is very simple--the variable just goes into the cells in column B and various formulas spit out results in subsequent columns. Here is the issues, in all of those other columns, I prefer that the columns remain blank until there is a number in the B cell. Right now, the formulas take an empty B cell as a 0 and go ahead a spit out a result. What can I do to keep those blank, even though the formula is there ready for data, until something is imputed?

You can use ISBLANK function + IF condition to achieve this.

=IF(ISBLANK(A3),"",A3+15)

This formula adds 15 to A3 only if A3 is not blank.

In your formula, you can check the value of column B:

=IF (B2 <> ""; B2 * 2; "")