Math Tips provided by

Carolyn McLain

Basic Training Educational Services, LLC

Divisible Numbers

Have you ever wanted an easy way to tell if one number was divisible by another number?  (A number is divisible if it is capable of being evenly divided, without a remainder.) I have listed a few clues to use when trying to find out if one number is divisible by another.

 A number is divisible

By 2: if it is even, meaning it ends in a 0, 2, 4, 6 or 8, for example 12, 46, or 80

By 3: if the sum of the digits of the original number is divisible 3,

 for example, 888 is divisible by 3 because 8+8+8 = 24 and 24 is divisible by 3

By 5:  if it ends in a 5 or 0, for example 45, 90

By 6:  if it is divisible by 2 (even) AND 3 (sum of digits is divisible by 3)

By 9:  if the sum of the digits of the original digits is divisible by 9

By 10:  if the last digit ends in a zero such as 10, 20, 30…

By 25:  if the last two digits end in 25, 50, 75 or 00 such as 125, 350, or 800

By 100:  if the last two digits end in 00 such as 100, 200, 300…

Calculating a Tip the Easy Way

Have you ever thought about how much to leave for a tip?  There is an easy way to figure out 15% or even 20% if you are a big tipper.  Remember 15% is 10% + 5%.

Say you want to leave a tip on a bill of $43.73.  To make the math easy, I like to round.  In this case I would round to $45.00.  To take 10%, move the decimal to the left one digit, giving you $4.50.  Then take 5% (this is half of 10%), and half of $4.50 is $2.25.  Now add the two together and you have $6.75.  That is your tip.

If you want to make it 20% take the $4.50 and double it, so you would leave a tip of $9.00.