How to use the RAND function
What is the RAND function?
The RAND function calculates a random real number greater than or equal to 0 and less than 1. The function is volatile.
Table of Contents
1. Introduction
What is random?
Each outcome of a random process cannot be predicted with certainty before it occurs. It is unpredictable.
Is the RAND function random?
No, it is pseudo-random. The generated value is not truly random.
What is pseudo-random?
Random numbers created by software like Excel are not truly random, they can be predicted. That is why they are called pseudo-random meaning they look like random values but they are not.
What is volatile?
The function is volatile meaning a new random real number is returned every time the worksheet is calculated.
What is the effect of volatile functions?
They may slow down your worksheet/workbook if you have many volatile functions.
When is the worksheet calculated?
Cells containing non volatile functions are only calculated once or until you force a recalculation, however, volatile functions are recalculated each time you type in a cell and press enter.
Can you stop recalculating a worksheet?
Yes, you can change a setting to manual recalculations.
- Go to tab "Formulas".
- Press with left mouse button on the "Calculation Options" button, a popup menu appears.
- Press with mouse on "Manual".
This stops the automatic recalculations.
How to force a recalculation?
Pressing F9 key will recalculate or refresh all the formulas and values in every worksheet of every workbook you have open.
Pressing Shift+F9 will only recalculate the formulas and values on the single worksheet you're currently viewing or active.
Pressing Ctrl+Alt+F9 is the quickest way to force a full recalculation of absolutely everything in all open workbooks, even if nothing has changed. It ignores whether changes were made or not and completely recomputes.
Are there more volatile functions in Excel?
Yes. OFFSET, TODAY, NOW among others.
| Function | Syntax | Description |
|---|---|---|
| OFFSET | OFFSET(reference, rows, cols) | Returns a cell offset from a reference cell. |
| TODAY | TODAY() | Returns the current date. |
| NOW | NOW() | Returns current date and time. |
| RANDARRAY | RANDARRAY([rows], [columns], [min], [max], [whole_number]) | Returns an array with random numbers. |
| RANDBETWEEN | RANDBETWEEN(bottom, top) | Returns a random whole number between bottom and top |
Note, that conditional formatting is extremely volatile or super-volatile meaning it is recalculated as you scroll through a worksheet.
What other functions return random values?
| Excel Function | Syntax | Description |
|---|---|---|
| RAND() | RAND() | Returns a random decimal number between 0 and 1 |
| RANDBETWEEN | RANDBETWEEN(bottom, top) | Returns a random whole number between bottom and top |
| RANDARRAY | RANDARRAY([rows], [columns], [min], [max], [whole_number]) | Returns an array with random numbers. |
2. Syntax
RAND()
The RAND function has no arguments.
3. Example 1
This basic example demonstrates what the RAND function outputs. The image above shows the RAND function in cells B3:B5, the output is a pseudo-random real number between 0 (zero) and 1.
Formula in cell B3:
The output values changes every time a new value is entered in any cell, this is why the function is a volatile function meaning it recalculates every time the worksheet recalculates. The RAND function takes no arguments, however you are still required enter the parentheses.
4. Example 2
A company is analyzing the distribution of customer wait times for their service. They've modeled the wait times using a normal distribution with a mean of 100 seconds and a standard deviation of 20 seconds. Use Excel's NORM.INV function with a random probability to generate a set of sample wait times. What is the distribution of these wait times, and how does it compare to the expected normal distribution?
What we can derive from the question:
- Random data follows a normal distribution.
- Mean: 100 seconds
- Standard deviation: 20
Formula in cell F19:
The formula in cell F19 and cells below returns random values based on a mean of 100 and a standard deviation of 20. A table to the left of the chart (columns A and B) showing the ranges and their corresponding counts. The table is a frequency table that contains the count based on ranges 57 to 141.
The image above shows a combination chart containing a column chart and a line chart. The blue columns represent the calculated distribution from source range B19:C31 and the black curve represents the normal probability density function.
The histogram shows a roughly bell-shaped distribution, with the peak around the 92-99 range, which aligns with the mean of 100 and standard deviation: 20 specified in the NORM.INV function. This charting technique allows us to compare the distribution to the expected normal distribution and find differences that may be problematic.
5. Example 3
A company is modeling the time it takes for customers to complete an online purchase process. They believe the completion times follow a beta distribution scaled between 10 and 90 minutes, with shape parameters α=8 and β=4. Use Excel's BETA.INV function with random probabilities and generate a set of sample completion times. What is the distribution of these completion times, and how does it compare to the expected beta distribution?
What we can derive from the question:
- Random data follows a beta distribution.
- shape parameter: α = 8 (alpha)
- shape parameter: β = 4 (beta)
- Lower limit: 10 [A]
- Upper limit: 90 [B]
The BETA.INV function has the following arguments: BETA.INV(probability,alpha,beta,[A],[B])
Formula in cell F19:
The formula in cell F19 and cells below returns random values based on a mean of 100 and a standard deviation of 20. The frequency table in cell range B19:C31 contains the count based on ranges 57 to 141.
The image above shows a combination chart containing a column chart and a line chart. The blue columns represent the calculated distribution from source range B19:C31 and the black curve represents the BETA probability density function.
The histogram shows a right-skewed distribution, with the peak around the 65-70 range, which is consistent with the beta distribution parameters given. The distribution is bounded between 10 and 90, with no values outside this range, reflecting the scaling parameters in the BETA.INV function.
This charting technique allows us to compare the distribution to the expected normal distribution and find differences that may be problematic.
'RAND' function examples
The RAND() function In Excel returns a number greater than or equal to 0 (zero) and less than 1. Combining […]
Microsoft Excel has three useful functions for generating random numbers, the RAND, RANDBETWEEN, and the RANDARRAY functions. The RAND function […]
Functions in 'Math and trigonometry' category
The RAND function function is one of 61 functions in the 'Math and trigonometry' category.
How to comment
How to add a formula to your comment
<code>Insert your formula here.</code>
Convert less than and larger than signs
Use html character entities instead of less than and larger than signs.
< becomes < and > becomes >
How to add VBA code to your comment
[vb 1="vbnet" language=","]
Put your VBA code here.
[/vb]
How to add a picture to your comment:
Upload picture to postimage.org or imgur
Paste image link to your comment.
Contact Oscar
You can contact me through this contact form