- Thread starter rpmc
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First calculate k....

Calculate P(Z <k) =0.90 ---(1)

where Z follows Standard Normal distribution.

you will get k as 1.28 ( check again)

Now you know P90 , say q

ie P(X<q) =.90 where X follows Normal distribution with mean (P50) and sd( we have to calculate now).

P( (X-mean)/sd <(q-mean)/sd) =0.90 -----(2)

using 1 and 2

k = (q-mean)/sd solve sd now...

Hello to all,

Similar question: for a lognormal distribution, P10, P50 and P90 are given. How do you calculate u and sigma?

Similar question: for a lognormal distribution, P10, P50 and P90 are given. How do you calculate u and sigma?

http://en.wikipedia.org/wiki/Log-normal_distribution

Without me stepping through it, you might have to solve simultaneous equations or use iteration.

This

http://en.wikipedia.org/wiki/List_of_logarithmic_identities

may come in handy.