MULTIPLYING BY 2½ Rule: Starting from the first digit of the given number, double each digit and add one-half the given digit. Ignore any fractions. Add any tens digits to the previous answer digit. Add 5 if the preceding digit of the given numb... Read more

The 11 Times Trick We all know the trick when multiplying by ten – add 0 to the end of the number, but did you know there is an equally easy trick for multiplying a two digit number by 11? This is it: Take the original number and imagine a space... Read more