Ask Dr. Math

Elementary Archive

Browse Elementary Multiplication
Stars indicate particularly interesting answers or good places to begin browsing.

Selected answers to common questions:
    Flashcards/worksheets on the Web.
    Learning to multiply.
    Least common multiple, Greatest common factor.
    Number sentences.
    Order of operations.

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Times Greater Than, Times As Much As [05/02/1999]

A number is five times greater than x. Will this number be 6x or 5x?

To Multiply or Divide? That Is the Question. [09/02/2003]

In a story problem, how do you know whether to multiply or divide?

Using Doubling to Multiply [02/20/2002]

Can you think of a way to use doubling to multiply 6 x 7?

Using the Distributive Property [08/23/2001]

My math teacher told us to work problems like this: a(b-c)= ab-ac.

Ways to Add and Divide More Easily [11/17/2008]

I have to add 2398 and 5752 and then divide by 37. I can do it, but it takes a long time. Is there any faster way to do those calculations?

What is 65 Times Ten Million? [3/29/1995]

What is 65 times ten million? Also, we've had pluses, multiples, and times. Are there going to be any new things after that?

What is 75% of $5000? [1/2/1995]

What is 75 percent of $5,000?

What is a Multiple? [12/4/1995]

What is the definition of a multiple?

What is multiplication? [11/09/1997]

What does multiplication have to do with addition, geometry, and real life?

Why Cancel? [02/25/2003]

Why do we have to cancel numbers?

Why Casting Out Nines Works [10/13/2008]

Can you explain in simple terms why the Casting Out Nines method works?

Why Does OF Mean Multiply? [12/04/2001]

I wanted to know why the word "of" means multiplication.

Why Is Mental Math Important? [03/25/2004]

How can I convince a 14 year old girl who is in 8th grade the importance of mental math? I think that skills like mentally adding and subtracting 2 digit numbers and being able to estimate multiplying 2 digit large numbers are critical. My daughter's teacher says that such skills aren't needed because of calculators and computers.

Why Multiplying by 10 Just Adds a Zero at the End [10/18/2005]

My 8-year old is having trouble understanding why multiplying by 10 just adds a 0 to the end of the number. Do you have any thoughts on how to explain it to her?

Why Rules? [08/15/2001]

Why do we need to have rules for order of operations?

The Zero Power of Two [12/10/1998]

Why is 2 to the 0 power equal to 1? I don't understand how a number can be multiplied by itself zero times.

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