A New Art Or The Lightning Interest Rules
Reduce the whole time to
months and set it down in figures; divide the number of days by three,
and set the quotient down to the right of the months, and multiply that
by the quotient of the money divided by two; the answer will be the
interest at six per cent. To change to any other rate, multiply the
interest by it and divide by six. $160--one year, seven months,
twenty-one days, at six per cent. $160--2--$80 x 197--$15.76 at 6.
Parties in New York are teaching this rule at $5 a scholar.