Given 1600 door knocks, you have a 50% chance of obtaining your required interviews. You need MORE thatn 1600 to get a 75% chance.
N is the number of doors needed.
Mean = N * 0.0937 = 150
Variance = N * 0.0937 * (1-0.0937)
There's enough that you probably can get away with a Normal Approximation.
What's next?
Sorry. that was a typo.. it should just be
I do not understand why we have only a 50% chance of obtaining the required interviews with N =1600?
And why is it that with N being the number of doors needed, you have mentioned that Mean = N * 0.0937 = 150. Doesn't this mean that N =1600???
Obscure hints aren't helping? I should try to be more clear.
You need a value, N, such that.
N*0.0937 = Mean > 150
N*0.0937*(1-0.0937) = Variance
SD = sqrt(Variance)
Mean - 0.67449*SD = 150
Your challenge, should you choose to accept it, is to tell me where I dreamed up that "-0.67449".