*How to become a Lightning Calculator by Anonymous is part of the HackerNoon Books Series. You can jump to any chapter in this book here. Short Method to Find the Interest of a Given Sum.*

## Short Method to Find the Interest of a Given Sum.

Reduce the time to months, and to the number thus found annex one-third of the days, which whole number multiplied by one-half of your principal will produce you the required interest in dollars, cents and mills, at 6 per cent. If days only are given, multiply one-third of the days by one-half of the principal for the required interest at 6 per cent. Note these exercises:

$250 at 6% for 8 mos. 6 ds. = 82 × 125 = $10.25.

$250 at 6% for 93 ds. = 31 × 125 = $3.88.

$250 at 6% for 9 mos. = 9 × 125 = $11.25.

In some respects this rule is superior to the well-known 60-day method of reckoning interest.

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