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

Selected answers to common questions:
    Flashcards/worksheets on the Web.
    Order of operations.
    Number sentences.
    Subtraction with borrowing/regrouping.

3rd Grade Math Struggle [1/5/1995]
My daughter is in 3rd grade. Up until this year, math was her favorite subject. Even though she struggled with it, she enjoyed it. . . This year is awful -- she can't seem to grasp the basics of subtraction. . . What can you suggest for someone who used to love math, but is fast developing a phobia? Any kind of fun exercises she could do, books I could get, or even computer programs.

Basic Real Number Properties [07/31/1997]
I need information about basic real number properties: associative, commutative, closure, identity, inverse, distributive.

Borrowing in Subtraction [12/01/1998]
When doing subtraction on problems like 100-99, why do the zeros become nines? How does that borrowing work?

Elapsed Time and the Grouping Factor [03/08/2003]
Why can't you just subtract the two times given in a word problem and get the time elapsed?

Introduction to Negative Numbers [08/11/1998]
What is 11 - 12? How can you subtract more than what you have?

Manipulating Positive and Negative Numbers [8/9/1996]
Could you explain the rules for adding, subtracting, multiplying, and dividing positive and negative numbers?

Multiples of 9 Number Puzzle [03/23/2003]
If you take a two-digit number, add the digits, and subtract the sum from the original number, why is the answer always a multiple of 9?

Order Of Operations in Four Steps [02/15/1998]
I need help figuring out what operation to do first.

Properties of Real Numbers [05/20/1997]
What are the associative, the commutative, and the zero product properties?

Signs: Rules, Number Line [07/13/2001]
What is (-) - (+) = ? or (+) + (-) = ?

Subtracting 999-100 [12/6/1994]
What is the answer to this: 999-100?

Subtracting Decimals with Borrowing [10/09/2001]
How do you subtract 488.354 from 536.30?

Subtracting Negative Integers - Number Line [10/15/1996]
How do you subtract integers like 5-(-6) ?

Subtracting Numbers by Walking a Number Line [09/12/2001]
For example: -8.1- -6.9 = -1.2 and -9.9- -11.1 = 1.2. All the numbers are negative, so why is the answer to the first problem negative but the second isn't?

Subtraction: Decomposition (Regrouping/Borrowing) [06/06/2003]
How do you subtract using the decomposition method?

Tips for Negative and Positive Numbers [11/30/2001]
I really get confused when adding a negative and a positive.

Working with Integers [01/12/1999]
Could you explain how to divide, multiply, add, and subtract integers?

Adding and Subtracting Integers [04/17/2006]
Can you explain how to add and subtract negative numbers?

Adding and Subtracting Measurements [08/13/1998]
How do you add and subtract measurements like 4'7" + 2'10" and 11'6" - 2'8"?

Adding and Subtracting Negative Numbers [02/07/2002]
What is (-1) - 5 + -8 equal to?

Adding and Subtracting Units of Time [12/11/1998]
How do you subtract units of time? In particular, how do you borrow from hours to make the minutes bigger?

Adding Negatives [12/04/1997]
What is -2 - 7/10 ? Is it -1 3/10 or -2 7/10?

Addition and Subtraction Patterns [09/22/2000]
In my fourth grade class we found patterns in addition problems, but when we tried this with subtraction it did not work...

Are Subtraction and Division Commutative and Associative Operations? [05/15/2008]
I don't agree that subtraction and division are not commutative operations. If we define a - b as a + (-b), then it commutes correctly into (-b) + a. So why does everyone say subtraction is not commutative?

Basic Subtraction [06/08/2001]
I need help with basic subtraction, like 15 - 9 = ?

Borrowing from Zero [06/01/2006]
How do you borrow to subtract from a lot of zeros, like 9000 - 584?

Borrowing in Subtraction in Various Contexts [10/25/2006]
An explanation of using borrowing to calculate 12 5/11 minus 2 6/11 is extended to borrowing when subtracting times, liquid measures, and other wholes and parts in general.

Brackets [01/29/2001]
Please explain how brackets [] work.

Calculating Timecards [08/03/1999]
Is there a formula to find how many hours a person worked?

Carrying and Borrowing [01/14/1998]
My son has a problem understanding addition and subtraction when he has to do regrouping, what I call carrying and borrowing...

Casting Out Nines to Check Arithmetic [08/26/1999]
Can you explain how to use the 'casting out 9's' technique in a way that a 6th grader can understand?

Comments on Dividing Fractions [03/15/2007]
A question on how to divide fractions leads into comments on how division and subtraction can be thought of as multiplication and addition of an "inverted" number.

Confusion over Interpretation of PEMDAS [03/24/2005]
Students take PEMDAS letter by letter, tending to do all multiplication before any division, rather than working from left to right. Here's a suggestion on how to help avoid that confusion.

Counting a Span Versus Finding a Difference between Two Numbers [06/03/2004]
Why is it that the difference between year 2012 and year 2003 equals 10 years but the difference between the numbers 2012 and 2003 equals 9?

Drawing Equations on the Number Line [05/09/2002]
How can I draw an equation like 2 - (-5) = 7 on a number line?

Equal Additions [11/01/1997]
What is the "Equal Additions" method of subtraction?

Evaluating Parentheses, Brackets, Braces and Grouping Symbols [01/20/2007]
How do I evaluate or simplify an expression with lots of grouping symbols, like (18/2){[(9 x 9 - 1)/ 2] - [5 x 20 - (7 x 9 - 2)]}?

Even More on Order of Operations [10/26/2017]
How can 8/4(3-1) have two answers? Doctor Peterson unpacks the ambiguities that have made the order of operations a persistent lightning rod for controversy — and misunderstanding.

Explaining Order of Operations [09/06/2001]
How would you explain the order of operations to a 5th or 6th grader who has not yet studied the subject?

Explaining Subtraction of Integers as Adding the Opposite [02/16/2007]
I'm trying to help my 7th grade class understand why subtracting an integer is the same as adding its opposite, particularly in cases like (-5) - (-3). Can you give real life examples or ideas on how to explain this to them?

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