No. One of 4 things can happen. 1) You get through on the first call: probability 1- .55= .45. 2) you get through on the second call: meaning you did NOT get through on the first call, prob. .55, but did on the second, prob .45. The probability of that is (.55)(.45)= .2475. 3) you get through on the third call. By the same argument the probabilty of that is (.55)(.55)(.45)= .136125. 4) It takes more than four calls. The probability you got through on the first, second, or third calls is 0.45+ 0.2475+ 0.1356125= 0.833625. The probability you do NOT get through in three calls is 1 minus that: 1- 0.833625= 0.166375.

Exactly the same answer. It doesn't matter who is calling!b. If, in addition, a friend tries independently to contact the same helpdesk, what is the probability that it will require more than three calls between you?

Yes, study! Memorize the basic formulas.Any pointers to help me get started here? thanks