Question

A recent study estimates that 45% of iPhone still have their phone within 2 years of purchasing it. Suppose you randomly select 30 iPhone users. Let random variable X denote the number of iPhone users who still have their original phone after 2 years.

A) Determine the probability that between 6 and 9 iPhone users still have their original phone after 2 years. Round to 3 decimal places.

Answer 1

Sample size , n =    30
Probability of an event of interest, p =   0.45

P ( X = 6) = C (30,6) * 0.45^6 * ( 1 - 0.45)^24=      0.0029
P ( X = 7) = C (30,7) * 0.45^7 * ( 1 - 0.45)^23=      0.0081
P ( X = 8) = C (30,8) * 0.45^8 * ( 1 - 0.45)^22=      0.0191
P ( X = 9) = C (30,9) * 0.45^9 * ( 1 - 0.45)^21=      0.0382

probability that between 6 and 9 iPhone users still have their original phone after 2 years

= 0.0029 + 0.0081 + 0.0191 +0.0382=0.068