Question 1042325
Let the xth call be the call that the first sale is made.  The support is then x = 1,2,3,4,5,.... .

===> Use the geometric distribution with pmf {{{p(x) = (1-p)^(x-1)*p = 0.83^(x-1)*0.17}}}

===> (a) {{{p(5) = 0.83^4*0.17 = 0.0807}}}, to three significant figures.

(b) {{{p(1) + p(2) + p(3) = 0.17 + 0.83*0.17 + 0.83^2*0.17 = 0.42821}}}, to five significant figures.


(c) {{{1-p(1) - p(2) - p(3) = 1 - 0.42821 = 0.57179}}}