# Basic Math Shortcuts

Here are some shortcuts I learned to make basic math easier, working with base numbers 0 to 9.

When 0 is multiplied or divided by any number, the answer is 0. When 0 is added to or subtracted from any number, the answer is that number. You cannot divide by 0.

When multiplying whole numbers that end in 0, they are called base 10 numbers. You can drop the 0, multiply the remaining number, then add the 0 back to your answer. For example, if you need to multiply 150 times 30, you can drop the 0 from both numbers and multiply 15 times 3 to get 45. Then add back the 2 zeros that were dropped (1 from each number) and your final answer is 4,500. This only works when 0 is at the end of the number. For example, you cannot drop the 0 and add it back if the number is 105. If you have 1,050 times 3, you can drop the 0 at the end, multiply 105 times 3 to get 315, then add the 0 back for a final answer of 3,150.

The number 1 is pretty simple. If you can count, you can add and subtract 1. If you multiply or divide by 1, your answer is the number that you are multiplying or dividing by 1. On the other hand, if you are dividing 1 by a number, the fraction is just 1 over that number because that is in its simplest form.

If you need to divide 1 by a number and get a decimal, here are some common ones to remember. 1 divided by 2 is the same as one half. Since the first decimal place is tenth, remember that half of 10 is 5, which gives you the answer .5 (or 0.5). If you need 2 decimal places, you look at half of 100, and just as you added a 0 to 10 to get to 100, you can add a 0 to the 5 and get .50 (or 0.50). 1 divided by 3 is .3 (or 0.3) and the 3 repeats indefinitely. Whatever decimal place you round it to will not change (.3 or .33 or .333, etc.). When dividing 1 by 4, think of the 1 as a whole dollar (1.00) and the 4 as a quarter because 1 divided by 4 is one quarter (or one fourth). You know it takes 4 quarters to make a dollar, so one quarter is 25 cents, or 0.25, two quarters are 50 cents, or half of a dollar, or 0.50. Three quarters, or three fourths, is 75 cents, or 0.75. Of course 4 quarters gives you the 1 whole dollar. Typically, you do not need to add a 0 to the right of the decimal place if it is the last number on the right. For example. 0.5000 is the same as 0.5. The extra zeros add no value, unless you are required to list them in your answer, like when you are showing currency (money), which should be shown with 2 decimal places.

1 divided by 6 gives you a decimal of .16 (or 0.16) and the 6 repeats , so it will eventually need to be rounded to 7, like 0.167, or 0.166667, or 0.17 if you need to round to the nearest hundred. Finally, 1 divided by 9 is 0.1 and the 1 repeats, just like the 3 above. When you round, you will just have ones like 0.11 or 0.111111.