Ask Dr. Math
Dr. Math Home ||
Middle School ||
High School ||
Dr. Math FAQ
See also the
Dr. Math FAQ:
order of operations
learning to multiply
3D and higher
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.
Order of operations.
- Proving That (-1) * (-1) = 1 [01/30/2006]
At the high school level it is difficult to prove that -1 x -1 = 1. Is
there a published proof somewhere that is appropriate for kids that age?
- Rapid Multiplication ... Diagonally? [02/24/2010]
Doctor Vogler describes the "accumulator" method for finding products
of two multi-digit terms, then works through an example.
- Rectangular Arrays to Teach Multiplication [11/10/1994]
I teach fourth grade math. Are rectangular arrays the best way to teach
- Russian Peasant Multiplication [08/19/1997]
I have a project to do on "Russian" or "peasant" multiplication.
- Russian Peasant Multiplication [11/01/1997]
What is Russian peasant multiplication?
- Square Numbers [07/27/1999]
Can you explain what a square number is?
- Squaring Two-Digit Numbers Ending in 5 [09/10/2001]
Take the first digit, multiply it by the next consecutive number, and
place it in front of 25. Can you prove this shortcut?
- Sum of Products [11/01/1999]
When a word problem refers to the sum of the products, what exactly does
- The Term Power [10/23/2001]
One of my students asked how we came to use the term power to express the
number of times we multiply a number by itself.
- 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
- 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.
Search the Dr. Math Library:
© 1994- The Math Forum at NCTM. All rights reserved.
Home || The Math Library || Quick Reference || Search || Help