Important This procedure replaces the numbers in the range with the result of the multiplication.
In an empty cell, enter the number that you want to multiply by.
Select the cell, and on the Edit menu, click Copy.
Select the range of numbers that you want to multiply.
On the Edit menu, click Paste Special.
Under Operation, click Multiply.
Click OK.
Delete the content of the cell entered in the first step.
Source:
http://office.microsoft.com/en-us/excel-help/multiply-numbers-HP003056141.aspx#BMmultiply_a_range_of_numbers_by_a_numb