-LN(1-p)/lambda
is the inverse of EXPONDIST(x,lambda,TRUE)

Jerry

Stuart Douglas  -

The exponential density function f(x) = lambda*EXP(-lambda*x),

or f(x) = EXPONDIST(x,lambda,FALSE).

The cumulative probability p = P(X<=x) = 1 - EXP(-lambda*x),

or p = P(X<=x) = EXPONDIST(x,lambda,TRUE).

For cumulative probability p = P(X<=x), the inverse cumulative is x
= -LN(1-p)/lambda.

-  Mike Middleton
http://www.DecisionToolworks.com
Decision Analysis Add-ins for Excel