Syntax
EXPONDIST(x, lambda, cumulative)
| Parameter | Description |
|---|---|
| x | Parameter of the EXPONDIST function. |
| lambda | Parameter of the EXPONDIST function. |
| cumulative | Parameter of the EXPONDIST function. |
Examples
Probability of waiting over 30 min
Formula
=1-EXPONDIST(30, 1/15, TRUE)
Returns ~0.1353. If arrivals happen every 15 min on average (lambda=1/15), there is about a 13.5% chance of waiting more than 30 minutes.
CDF at the mean
Formula
=EXPONDIST(10, 0.1, TRUE)
Returns ~0.6321. At x equal to the mean (1/lambda = 10), the CDF is always about 63.2% for an exponential distribution.
Density function value
Formula
=EXPONDIST(5, 0.5, FALSE)
Returns ~0.0410. The probability density at x=5 when lambda=0.5.
Common Errors
#NUM!
x must be non-negative and lambda must be positive.
#VALUE!
Non-numeric arguments trigger this error.
Tips
Upgrade to EXPON.DIST
EXPONDIST is the compatibility function. Use EXPON.DIST in new work for consistency with other modern distribution functions.
Complement for 'at least' questions
To find P(X > x), use =1 - EXPONDIST(x, lambda, TRUE). The exponential CDF gives the probability of being at or below x.
Relationship to Poisson
If events follow a Poisson distribution with rate lambda, then the waiting time between events follows an exponential distribution with the same lambda.
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