+ 134 (1-0251"- 1) Pi ^ -025 - 80 (300 + 120) ; 



CUERENT RATE OF INTEREST. 157 



But also P = {S- S,) I'Op'' = 104 X 1-025^5 ^ 31,- shillings. 



(3.) Calculate the profit of a normal series of age grada- 

 tions, that is to say, for the strictly annual working. 



Total Profit = """'""F, - '""-'""'F,. 



Now, '""■"-' F, = S. + ™'G, = 80 X 404 +91,360 (see 

 page 142). 



vormai-^^ _ 123,860 sMlUngs, 

 while 



normal J^ Q _1_ normal ri . 



S, = 80 X 300 = 24,000 shillings. 



-'"■>'""G,= [(300 + 120 + 60) (1-025^"- 1) - 1 5 X (1-0255" - 1) 



+ 44 (1-025^" - 1) + 87 (1-02530- 1) + 118 (1-025'-^^'- 1) 



-Dp, ^-025 -80 (£ 



«'-""'VV, = 73,836 shillings, 

 hence — 



normal j^.^^ 24,000 + 73,836 = 97,836 shillings, 



and 



Profit = 123,860 - 97,836 = 26,024 shillings. 



2. Determination of the Rate of Interest yielded hy the Cajntal 

 invested in Forestry, called the Forest Per cent. 



a. Ciilriilaiion for ihc Tnicrmittent WorJriiir/. 

 Under the intermittent working, the rate of interest changes 

 from year to year, because the capital, as well as the increment, 

 change with the advancing age of the wood ; hence, it is neces- 

 sary to distinguish between the current annual and the mean 

 (or average) annual rate of interest. 



i. Current Annual Rate of Interest. 



As indicated on page 113, the rate of interest is expressed 

 by the fraction 



Kate of interest = — . 

 C 



