Generating Random Numbers in Excel with a Fixed Sum
When working with Excel, one common challenge is generating random numbers for which you need to maintain a fixed sum. This can be particularly useful in financial modeling, forecasts, and simulations. In this article, we will guide you through a step-by-step process to achieve this.
Step-by-Step Instructions
To generate random numbers in Excel for two columns such that their sum equals a target value from another column, follow these steps:
Set Up Your Spreadsheet
Assume your target values are in column A starting from A2. You will generate random numbers in columns B and C.Generate Random Number in Column B
In cell B2, enter the following formula to generate a random integer between 0 and the target value in A2:
RANDBETWEEN(0, A2)In cell C2, enter the formula to ensure the sum equals the target value:
A2 - B2This formula calculates the value for column C so that the sum of B2 and C2 equals the target value in A2.
Copy Down the Formulas
Select cells B2 and C2, then drag down the fill handle (the small square at the bottom right corner of the selection) to fill the formulas for all rows corresponding to your target values in column A.
Refresh Random Numbers
Each time the worksheet recalculates (e.g., by pressing F9), new random numbers will be generated in column B. Column C will automatically adjust to ensure the sum remains equal to the target value.
Example
ABC 1003763 20045155 502030In this example, the sum of columns B and C for each row equals the target value in column A.
Note
For generating decimal random numbers, use:
B2 A2 - RAND() * (A2 - 0) 0 C2 RAND() * (A2 - 0) 0The values in column B will be random but the values in column C will always balance them out to meet the target value in column A. This method ensures that you have a reliable way to generate random values while maintaining the required sum condition.
Additional Tips
If you need to handle a range from C1 to C10, you can use:
A1 RANDBETWEEN(MIN(C1:C10), MAX(C1:C10)) B1 C1 - A1Drag the formulae down from A1 and B1 to apply to all cells in the range.
By following these instructions, you can easily generate random numbers with a fixed sum in Excel, ensuring your data meets your specific requirements.