In: Economics
We use the present worth method
PW (0%) = -1000 + 250(P/F, 0%, 1) + 449(P/F, 0%, 2) + 800(P/F, 0%, 3) + 500(P/F, 0%, 4) + 500(P/F, 0%, 5)
= -1000 + 250*(1 + 0%)^-1 + 449*(1 + 0%)^-2 + 800*(1 + 0%)^-3 + 500*(1 + 0%)^-4 + 500*(1 + 0%)^-5
= 1499
PW (5%) = -1000 + 250*(1 + 5%)^-1 + 449*(1 + 5%)^-2 + 800*(1 + 5%)^-3 + 500*(1 + 5%)^-4 + 500*(1 + 5%)^-5
= 1139.536
PW (10%) = -1000 + 250*(1 + 10%)^-1 + 449*(1 + 10%)^-2 + 800*(1 + 10%)^-3 + 500*(1 + 10%)^-4 + 500*(1 + 10%)^-5
= 851.37
PW (15%) = -1000 + 250*(1 + 15%)^-1 + 449*(1 + 15%)^-2 + 800*(1 + 15%)^-3 + 500*(1 + 15%)^-4 + 500*(1 + 15%)^-5
= 617.38
PW (20%) = -1000 + 250*(1 + 20%)^-1 + 449*(1 + 20%)^-2 + 800*(1 + 20%)^-3 + 500*(1 + 20%)^-4 + 500*(1 + 20%)^-5
= 425.17
PW (30%) = -1000 + 250*(1 + 30%)^-1 + 449*(1 + 30%)^-2 + 800*(1 + 30%)^-3 + 500*(1 + 30%)^-4 + 500*(1 + 30%)^-5
= 131.85
PW (35%) = -1000 + 250*(1 + 35%)^-1 + 449*(1 + 35%)^-2 + 800*(1 + 35%)^-3 + 500*(1 + 35%)^-4 + 500*(1 + 35%)^-5
= 18.74
It then appears that at i = 40%, PW should turn negative
PW (40%) = -1000 + 250*(1 + 40%)^-1 + 449*(1 + 40%)^-2 + 800*(1 + 40%)^-3 + 500*(1 + 40%)^-4 + 500*(1 + 40%)^-5
= -77.68
Now find the i* at which PW = 0
Use interpolation
i*% = 35% + (40% - 35%)*(18.74/(18.74+77.68)) = 35.97%
Hence the relevant range for the interest rate is from 0% to 35.97%.