First year: 20
Second year: 20 years old
Third year: 20 years old
Year 4: 20
Fifth year: 25 years old
(2) 4+( 100-20*4)/25=4.8 years.
(3) 100=20*(P/A，I，5)+5*(P/F，I，5)
Let I =1%PV = 20 * 4.8534+5 * 0.9515 =10/.83.
Let I = 2% PV = 20 * 4.7135+5 * 0.9057 = 98.9.
(I- 1%)/(2%- 1%)=( 100- 10 1.83)/(98.9- 10 1.83)
i= 1.62%
(4) NPV =-100+20 * 3.7908+5 * 0.6209 =-21.08.