Telephone sales have
skyrocketed this past month. The
probability that 1 of the 4 telephone lines is busy is 75%. Therefore, currently the probability of all 4
lines being busy at the same time is about 32%.
I want to reduce the probability of all telephone lines being busy at
the same time.If I add 2 more telephone
lines, how much do I reduce the probability of all telephone lines being busy
at the same time? (Assume the probability that any phone line is busy remains at 75%)

Thank you for the opportunity to help you with your question!

he probability that 1 of the 4 telephone lines is busy is 75% so the probability of all 4 lines being busy at the same time is 75%*75%*75%*75% = 32% so adding 2 more phone lines, with line busy remains at 75% will give you 75%*6 = 18%

Please let me know if you need any clarification. I'm always happy to answer your questions.