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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Identity Element [10/12/2001]

What is an "identity element"?

Incorrect Application of PEMDAS and Order of Operations [09/14/2006]

My students think PEMDAS means that all addition should be done before any subtraction is done. How can I show and convince them that they need to do both operations at the same time working from left to right?

Is the 2 Related to the Numbers in Parentheses? [10/05/2001]

Order of operations: Which is the correct way to solve this problem: 36/2(8-5) = ? What's a comparable English sentence?

Large Arithmetic Problem [6/2/1995]

What is 784756895786 * 37846738654765485 + 547847358743 ?

Lattice Method of Subtraction? [06/13/2006]

I've learned about the lattice method of addition and multiplication. Is there a lattice method of subtraction?

Learning Addition and Multiplication with Algebra [3/16/1996]

How do you know what the (a) is in algebra? I saw this on a picture: a(1/a) = 1/a(a) = 1...

Learning the Times Tables [10/12/2008]

I have a hard time with the times tables, and so I don't enjoy math. Is there an easy way to get better at them?

Learning Times Tables [12/06/2005]

I'm having trouble learning my times tables. Can you give me any help?

Learning to Multiply and Divide Quickly [9/28/1995]

Do you have any ideas how I can learn to multiply and divide faster?

Learning to Multiply Three-Digit Numbers [07/03/1998]

I would like to learn how to do multiplication of bigger numbers, like 120 x 743.

Least Common Multiple [09/29/2001]

What is the least common multiple of 11, 13, and 17?

Least Common Multiple with Zero [03/26/2003]

I'm trying to find any reference about the least common multiple of two numbers when one (or both) is zero.

Lengths in Pictures [4/5/1996]

A picture of an insect is k times the actual size. If the leg on the picture is 3cm long, how long is the leg on the actual insect?

Lining Up Decimal Points [03/03/2003]

Why do we line up decimal points for addition and subtraction but not for division and multiplication?

Macintosh Elementary Math Software [01/14/1997]

Internet resources and information for multiplication/computation.

Massive Multiplication! [11/2/1994]

A first-grader wants to know if Dr. Math is good at multiplication.

Meaning of Multiplying Fractions [12/09/1999]

What does it mean to multiply a fraction by a fraction?

The Meaning of Powers, such as Squares and Cubes [3/14/1996]

What does the power mean? Like 5 to the power of 2?

Memorizing Multiplication Tables [2/26/1996]

I'm a 3rd grade teacher and my lesson is on 6x7, 6x8, and 7x8 in multiplication. I only know a trick for memorizing 7x8. Do you have any suggestions for 6x7, 6x8 and others?

Mental Math [07/25/2003]

I would like to find a trick for multiplying by 3367.

Multiples [11/08/2001]

What is the most common multiple of 13 and 7? I have no clue what they are even talking about.

Multiples of Four [03/01/1999]

Is zero a multiple of four?

Multiplicand, Multiplier [07/05/2001]

Do you agree with me that in the following mathematical sentence: 456x10, 456 is called the multiplicand and 10 is called the multiplier?

Multiplication [02/11/1999]

How many decimal places should the product of 3.26 and 0.25 contain?

Multiplication Before Addition [5/31/1996]

1000 * 20000 + 34 - 4023 = ?

Multiplication Facts [02/12/2002]

Can you use the same multiplication fact to find 4x50 and 5x40? What is a multiplication fact?

Multiplication of Fractions [03/22/1999]

What are cancellations?

Multiplication Signs [10/07/2002]

Why are there different ways to indicate multiplication?

Multiplication Tables on the Web [11/24/1996]

Can you tell me where I can find the multiplication tables on the WWW?

Multiplication Trick [02/08/1998]

When I multiply 25x25 I can do the answer in my head by multiplying the first digit times the next highest number and then writing 25. Why does this work?

Multiplier, Sum, Difference, Product, Quotient, Dividend [11/25/1997]

What is a multiplier? an addend? a minuend? a product? Why is the number that is being divided the "dividend"?

Multiply: 16 x 200 [12/6/1994]

I want to know the answer to the problem sixteen times two hundred.

Multiplying 3+9 [11/15/1994]

A well-nested problem.

Multiplying a 3-digit Number by a 2-digit Number [10/10/1995]

What is 697x56?

Multiplying and Dividing Negatives [07/20/1998]

Can you explain multiplication and division with signed numbers? For example what is the sign when you multiply negative numbers?

Multiplying a Number by Zero [09/14/2001]

When any number is multiplied by zero, why is the result zero?

Multiplying Billions [12/17/1997]

How do you multiply 50 billion by 55 septillion?

Multiplying by 1 [09/01/1998]

Why doesn't a number change when you multiply it by 1?

Multiplying by 1000 [03/10/1997]

What is 2,542 times 1,000?

Multiplying by 11 [09/16/1997]

We said: 568 x 11 and after about 5 seconds she said the answer was 6248. How did she do it so quickly?

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