SHORT METHODS OF MULTIPLICATION.
For certain classes of examples in multiplication short methods may be employed and the labor of calculation reduced, but of course for the great bulk of multiplications no practical abbreviation remains. A person having much multiplying to do should learn the table up to twenty, which can be done without much labor.
To multiply any number by 10, 100, or 1000, simply annex one, two, or three ciphers, as the case may be. If it is desired to multiply by 20, 300, 5000, or a number greater than one with any number of ciphers annexed, multiply first by the number and then annex as many ciphers as the multiplier contains.
TABLE.
5 cents equal 1/20 of a dollar.
10 cents equal 1/10 of a dollar.
12-1/2 cents equal 1/8 of a dollar.
16-2/3 cents equal 1/6 of a dollar.
20 cents equal 1/5 of a dollar.
25 cents equal 1/4 of a dollar.
33-1/3 cents equal 1/3 of a dollar.
50 cents equal 1/2 of a dollar.
Articles of merchandise are often bought and sold by the pound, yard, or gallon, and whenever the price is an equal part of a dollar, as seen in the above table, the whole cost may be easily found by adding two ciphers to the number of pounds or yards and dividing by the equivalent in the table.
Example. What cost 18 dozen eggs at 16-2/3c per dozen?
| 6 | ) | 1 | 8 | 0 | 0 |
| _ | _ | _ | _ | _ | |
| $ | 3 | . | 0 | 0 |
Example. What cost 10 pounds butter at 25c per pound?