611 OF ENGINEERING FORMULÆ.
Interest (Simple and Compound), Annuities, &c.
P — Principal in £ sterling.
n = Number of years, integral or fractional.
R = Amount of £1 at given rate per cent.
r — Interest „ „ „
1 = Interest; M = Amount; D = Discount; W = Present
worth.
A = Annuity to continue for n years.
V = Present value of an annuity.
Simple Interest, I = Pnr; M — P (1 + nr);
Compound Interest, M = P R”-
Annuities (Simple Interest), M = n A~(l + n~l r);
, , n — 1
WA(1 + ~^—r)
pn ___ y
Annuities (Compound Interest), M = ——.— A ;
Dubation, or Fibst Cost.
y = First cost of less durable article.
æ = First cost of more durable article to be on an equality
with »/.
N ~ Number of years’ duration of æ.
n = Number of years’ duration of y.
i — Rate of interest per annum in decimals of 100; for
example, 5 per cent. = *05.
(1 + i)N- 1
a; = y-------—•
(1 + t)N-(l + i)N~”
Valve of a; at different rates of interest (y = 1).
Duration, Years. X at Bates of Interest per Cent, per Annum.
n N 8 4 6 6
2 10 4'46W 4'3029 4-1639 4-0142
e 20 3'2491 3-0541 2-8783 2-7231
10 so 3-0162 2-6485 2-8644 2*1416
20 100 2-1287 1-8031 1-5926 1-4487
2 b 2