Generating Double-Digit Random Numbers

Venkataramanan needs to generate random numbers in the range of -99 to +99, excluding single-digit numbers (-9 to +9). He wonders if there is a way to accomplish the task.

There are a couple of worksheet functions that are often used to generate random numbers in Excel. The RAND function is used to generate a random number between 0 and 1, while the RANDBETWEEN function (part of the Analysis ToolPak) is used to generate a random number within a range of numbers.

There is no function to do what Venkataramanan wants to do, but you can write a formula that will do the trick. Consider this formula:

=IF(RAND()>0.5,1,-1)*(RANDBETWEEN(10,99))

The first RAND function determines if the result is '+' or '-' and the next RANDBETWEEN function returns the desired number between 10 and 99. When the function is done, you have the desired double-digit random number.

Another formula is similar in nature:

=ROUND(RAND()*89+10,0)*((RAND()<0.5)*2-1)

The first part generates whole numbers in the range of 0 through 89. The formula adds 10 to this, effectively giving a number from 10 to 99. The second part of the formula is then used to randomly determine whether the result should be positive or negative.

Another approach relies entirely on the RANDBETWEEN function and doesn't use any multiplication:

=VALUE(IF(RANDBETWEEN(0,1)=0,"-","")&RANDBETWEEN(1,9)&RANDBETWEEN(0,9))

The formula puts together a string that consists of either a minus sign or a blank followed by two digits. The formula then uses the VALUE function to convert the string to a numeric value. An even shorter version of the formula would be this:

=VALUE(IF(RANDBETWEEN(0,1)=0,"-","")&RANDBETWEEN(10,99))

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (3403) applies to Microsoft Excel 97, 2000, 2002, and 2003. You can find a version of this tip for the ribbon interface of Excel (Excel 2007 and later) here: Generating Double-Digit Random Numbers.