368 Mr Goodwyn on a Method of Calculating Interest. 
The amount of any Annual Salary, for any given number of days, may also be readily 
found by the foregoing Table, as follows: — Having found in it the interest of £1, at 1 per 
cent, per annum., for the given number of days, multiply that interest by the annual salary, 
and remove the decimal point two places to the right : the product, so altered, is the answer. 
Example . — Required the amount, for 155 days, of an annual salary of £20. 
Since £ *00424657534 is the interest of £ 1 at 1 per cent, per annum for 155 days, and 
*00424657534 X 20= *0849315068, &C. by removing the decimal point two places 
to the right, the product will become 8*49315068, &c. the answer. And this answer is 
the same as that for the interest of £ 400 at £ 5 per cent. (= £ 20 per annum ) for 155 days. 
In practice, it will rarely, if ever, be requisite to take out more of the decimal digits 
than will be sufficient, when multiplied by the given principal, to produce three, or at the 
mo^t four, decimal digits in the product ; as that number will give the answer to the nearest 
farthing. So, in the first example, at £ lU per cent., seven, or even six, digits will be 
quite sufficient. Thus, 
{U 
(■00«4<i5| 
t '0212325 j 18 
•6986 I 
4931 ( 
the answer. 
It will, moreover, greatly expedite the whole process to be able mentally and instanta. 
' , or any other decimals of a pound Sterling, into 
neously to convert the above 
{■ 
4931 I 
shillings, pence, and farthings ; and the reverse : operations, of which the mode may 
easily be learned from almost every treatise on decimal arithmetic. In the above instance, 
1:13:11| 
8: 9:10i 
accuracy, can scarcely be produced from any of the voluminous Tables of Interest that have 
come under the Calculator’s observation. An additional advantage may be gained by means 
of Contracted Multiplication in finding the products ; as will be evident from a few examples. 
( 1-6986 1 _ « f 
I 8-4931 j - 1 
Results may thus be obtained, which, for ease and 
Example I. 
Required the Interest on £375 for 155 days 
at 5 per cent, per annum ? 
155 days, per Table, at £ 5 per cent. 
^ *02 4- G a = *0212328 &c. which being 
multiplied by 375, or 
rather, when prepar- 
ed for contract, mul. by 573 
636984 
148630 
106 16 
will produce 7.96230 =r£7: 19:3 Ans* 
Example II. 
Required the Interest on £ 4287, 10s. for 
359 days at £ 5 per cent, per annum ? 
359 days, per Table, at £ 5 per cent. 
r= *04 4 F e — ■ 0*491 7808 &c. which being 
multiplied by £ 4287, 10s. 
4287*5, or ra- 
ther by 5*7824 
1^71232 
983562 
393424 
34425 
2459 
will produce 210*85102 ~£210 : 1 7: Oi Ans. 
Example III. 
Required the Interest on £ 1630, lOs. for 
207 days at 3g per cent, per annum? 
207 days, per Table, at £ 1 per cent. 
=*005 4i/e- *00567123 
3g per cent.—S'5, multiplying by 
which , or rather by 5*3 
1701369 
283561 
the result is *01984930 
£ 1630 10^ £ 1630*5, or ra- 
ther when prepa- red for contract- 
ed multiplication, 5*0361 
1984930 
1190958 
59548 
992 
will produce 32*36428=:£32:7 :34 Ans. 
It is manifest from the above Examples, that the use of the Table is not confined to any 
particular Principal or fixed Rate of Interest. Nor, excepting in so far as regards inspection, 
is it limited to any determinate Number of Days ; for, when the Interest of any given Sum, 
at any given Rate, has been found for one day, it is evident, that the interest of that same 
Sum, at the given Rate, for any given Number of Days, must be the Interest so found for 
ONE DAY multiplied into the given Number of Days. 
