In 2009 Apples share of laptops and desktops priced above 10

In 2009, Apple’s share of laptops and desktops priced above $1000 and sold in US retail outlets was 89%. Answer the following questions based on a random sample of seven laptops and desktops priced above $1000: What is the probability that less than five of the computers were produced by Apple?

Solution

FEWER THEN 5 CAN BE CALCULATED BY 1 - P(5) -P(6)-P(7)

PROBABILITY OF APPLE SHARE = 0.89

PROBABILITY OF NON APPLE = 0.11

TOTAL SAMPLE = 7 LAPTOPS

P(5)=7C5(0.89^5)(0.11^2)=0.1419

P(6)=7C6(0.89^6)(0.11)=0.3827

P(7)=0.89^7=0.4423

ADDING P(5)+P(6)+P(7) = 0.9669

The probabilitY OR LESS THEN 5 is 1-0.9669=0.0331.