Syntax
EXPON.DIST(x, lambda, cumulative)
| Parameter | Description |
|---|---|
| x | Parameter of the EXPON.DIST function. |
| lambda | Parameter of the EXPON.DIST function. |
| cumulative | Parameter of the EXPON.DIST function. |
Examples
Probability of next customer within 5 min
Formula
=EXPON.DIST(5, 0.2, TRUE)
Returns ~0.6321. If customers arrive at a rate of 0.2 per minute (one every 5 min on average), there is a 63.2% chance the next one arrives within 5 minutes.
Failure rate density at 100 hours
Formula
=EXPON.DIST(100, 0.01, FALSE)
Returns ~0.00368. This is the probability density (not probability) at exactly 100 hours for a component with failure rate 0.01 per hour.
Probability server responds within 2 seconds
Formula
=EXPON.DIST(2, 1.5, TRUE)
Returns ~0.9502. With an average response rate of 1.5 per second, there is a 95% chance of responding within 2 seconds.
Common Errors
#NUM!
x must be >= 0 and lambda must be positive. Negative values for either cause this error.
#VALUE!
Occurs if arguments are non-numeric text.
Tips
Lambda is the rate, not the mean
Lambda is the rate parameter (events per unit time). If the average time between events is 10 minutes, lambda = 1/10 = 0.1.
Memoryless property
The exponential distribution is memoryless: the probability of waiting another 5 minutes is the same whether you have already waited 1 minute or 100 minutes.
Use cumulative for 'within' questions
Set cumulative=TRUE for questions like 'what is the probability it happens within x time.' Use FALSE only when you need the instantaneous density.
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