Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

31500

375764 (31500

11.929+ weeks. Ans.

60764

31500

292640

283500

91400

63000

284000

283500

500

Instead of reducing the divisor to ten-thousandths, we may reduce the dividend to hundredths. 37.5764 are 3757.64 hundredths of a bushel. The decimal .64 in this, is a fraction of an hundredth.

3.15 are 315 hundredths. Now the question is, to find how many times 315 hundredths are contained in 3757.64 hundredths.

3757.64 (315

315

11.929+ weeks. Ans. as before.

607

315

2926

2835

914

630

2840

2835

5

From the two last examples we derive the following rule for division: When the dividend contains more decimal places

than the divisor: Reduce them both to the same denomination, and divide as in whole numbers.

N. B. There are two ways of reducing them to the same denomination. First, the divisor may be reduced to the same denomination as the dividend, by annexing zeros, and taking away the points from both. Secondly, the dividend may be reduced to the same denomination as the divisor, by taking away the point from the divisor, and removing it in the dividend towards the right as many places as there are in the divisor. The second method is preferable.

The same result may be produced by another mode of reasoning. The quotient must be such a number, as being multiplied by the divisor will reproduce the dividend. Now a product must have as many decimal places as there are in the multiplier and multiplicand both. Consequently the decimal places in the divisor and quotient together must be equal to those in the dividend. In the last example there were four decimal places in the dividend and two in the divisor; this would give two places in the quotient. Then a zero was annexed in the course of the division, which made three places in the quotient. The rule may be expressed as follows:

Divide as in whole numbers, and in the result point off as many places for decimals as those in the dividend exceed those in the divisor. If zeros are annexed to the dividend, count them as so many decimals in the dividend. If there are not so many places in the result as cre required, they must be supplied by writing zeros on the left.

Division in decimals, as well as in whole numbers, may be expressed in the form of common fractions.

What part of .5 is .3?
What part of .08 is .05?
What part of .19 is .43 ?
What part of .3 is .07?

Ans..

Ans.

Ans. 43.

To answer this, .3 must be reduced to hundredths. 3 is 30, the answer therefore is

What part of 14.035 is 3.8?

3.8 is 3.800, the answer therefore is 3800

14035°

In fine, to express the division of one number by another, when either or both contain decimals, reduce them both to the

lowest denomination mentioned in either, and then write the divisor under the dividend, as if they were whole numbers.

[ocr errors]

Circulating Decimals.

XXIX. There are some common fractions which cannot be expressed exactly in decimals. If we attempt to change to decimals for example, we find .3333, &c. there is always a remainder 1, and the same figure 3 will always be repeated however far we may continue it. At each division we approximate ten times nearer to the true value, and yet we can never obtain it..1666, &c.; this begins to repeat at the second figure. = .545454, &c.; this repeats two figures. In the division the remainders are alternately 6 and 5.3 .168168, &c.; this repeats three figures, and the remainders are alternately 56, 227, and 272. Some do not begin to repeat until after two or three or more places. It is evident that whenever the same remainder recurs a second time, the quotient figures and the same remainders will repeat over again in the same order. In the last example for instance, the number with which we commenced was 56; we annexed a zero and divided; this gave a quotient 1, and a remainder 227; we annexed another zero, and the quotient was 6, and the remainder 272; we annexed another zero, and the quotient was 8, and the remainder 56, the number we commenced with. If we annex a zero to this, it is evident that we shall obtain the same quotient and the same remainder as at first, and that it will continue to repeat the same three figures for ever.

It is evident that the number of these remainders, and consequently the number of figures which repeat, must be one less than the number of units in the divisor. If the fraction is, there can be only six different remainders; after this number, one of them inust necessarily recur again, and then the figures will be repeated again in the same order,

[blocks in formation]

3

Whenever we find that a fraction begins to repeat, we may write out as many places as we wish to retain, without the trouble of dividing.

As it is impossible to express the value of such a fraction by a decimal exactly, rules have been invented by which operations may be performed on them, with nearly as much accuracy as if they could be expressed; but as they are long and tedious, and seldom used, I shall not notice them. Sufficient accuracy may always be attained without them.

I shall show, however, how the true value of them may always be found in common fractions.

The fraction reduced to a decimal, is .1111... &c. Therefore, if we wish to change this fraction to a common fraction, instead of calling it, or, which will be a value too small, whatever number of figures we take, we must call it. This is exact, because it is the fraction which produces the decimal. If we have the fraction .2222.. &c. it is plain that this is twice as much the other, and must be called. If & be reduced to a decimal, it produces .2222 .. &c. If we have 3333.. &c. this being three times as

1

much as the first, is

If be reduced to a decimal, it produces .3333.. &c. It is plain, that whenever a single figure repeats, it is so many ninths.

Charge .4444 &c. to a common fraction. Ans. 4.
Change .5555 &c. to a common fraction.

Change .6666 &c. to a common fraction.

Change .7777 &c. to a common fraction.
Change .9999 &c. to a common fraction.
Change .5333 &c. to a common fraction.

This begins to repeat at the second figure or hundredths. The first figure 5 is; and the remaining part of the fraction is of, that is, ; these must be added to

gether.

8

5

[ocr errors]

is 15, and

makes

The answer is If this be changed to a decimal, it will be found to be .5333 &c.

If a decimal begins to repeat at the third place, the two first figures will be so many hundredths, and the repeating figure will be so many ninths of another hundredth.

Change .4666 &c. to a common fraction.
Change .3888 &c. to a common fraction.
Change .3744 &c. to a common fraction.
Change .46355 &c. to a common fraction.

If be changed to a decimal, it produces .010101 &c. The decimal .030303 &c. is three times as much, therefore it must be 3. The decimal .363636 &c. is thirty-six

times as much, therefore it must be 36

[ocr errors]

27

999

If be changed to a decimal, it produces .001001001 &c. The decimal .006006 &c. is 6 times as much, therefore it must be 333 The fraction .027027 &c. is twenty-seven times as much, and must be TiT The fraction .354354 &c. is 354 times as much, and must be 35411. This principle is true for any number of places. Hence we derive the following rule for changing a circulating decimal to a common fraction: Make the repeating figures the numerator, and the denominator will be as many 9s as there are repeating figures.

If they do not begin to repeat at the first place, the preceding figures must be called so many tenths, hundredths, &c. according to their number, then the repeating part must be changed in the above manner, but instead of being the frac tion of an unit, it will be the fraction of a tenth, hundredth, &c. according to the place in which it commences.

Instead of writing the repeating figures over several times,

« ΠροηγούμενηΣυνέχεια »