Math Tip of the Day: Multiply and Divide with Zeros

Sometimes you have to multiply or divide numbers that have many zeros for digits.  Yes, you can do the traditional thing of multiplying against and dividing into every zero.  That can be time-consuming depending on the number of digits.  Or you can use a simple trick to make it a little easier.

Multiply and Divide with Zeros

 

When multiplying, multiply the whole numbers first.  Write down the product.  Then count the total number of zeros in the multiplicand and the multiplier (refer to this post for more information about multiplication).  Add that many zeros to the end of your product and you have your answer.  Ex.  6,000 x 50.  6 x 5 = 30.  So you write down 30.  The total number of zeros is four.  Write four zeros at the end of the product and your final answer is 300,000.  Multiply and Divide with Zeros 2

 

When dividing, divide the whole numbers first.  Write down the quotient.  Then count the total number of zeros in the divisor and the dividend.  Remove a pair of zeros from the divisor and the dividend until there are no more pairs left (I usually cross through each pair with a line).  Then the remaining zeros will be added to your  quotient.    Ex.  12,000/40.  12/4 = 3.  So you write down 3.  Then you can cross out one pair of zeros.  This leaves two zeros.  Your final answer is 300.

Was that easy?!  Now try it for yourself.  

18,000/200 and  700 x 20