Chapter 13 - General Rules of Probability - Apply Your Knowledge - Page 307: 13.3

Since 13% of the sites are lost after 2 years, we have P(site is lost after 2 years) = 0.13 P(all 7 references still good 2 years later) = [1 - P(site is lost after 2 years)]$^{7}$ $= [1 - (0.13)]^{7}$ $= (0.87)^{7}$ $= 0.377$

as given above