Binomial formula - solve for N help ...


I'm not a student and this is not for a test. I'm a programmer and this is related to the markets.

This is a link for the common formula:


How would you change the formula to solve for N?

Example: A doctor thinks that, when treated with a new drug, a
patient has a probability of 2/5 to improve. How many
patients must he treat to be sure (at p>.95 ) that at least one
patient will improve?

Thank you!