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number sense
ELEMENTARY
Arithmetic
addition
Browse Elementary Number Sense/About Numbers
Stars indicate particularly interesting answers or good places to begin
browsing.
Selected answers to common questions:
About zero.
Multiplying by zero.
Casting out nines.
Classifying numbers.
Googol, googolplex.
Number facts from the Web.
1 and 0: Prime or Composite? [10/06/1997]
Is the number one a prime or a composite number?
Why? What about zero?
Adding and Subtracting Roman Numerals [10/07/1997]
Do you have any suggestions for how to teach adding
and subtracting of Roman numerals?
Adding in Base 9 and Base 5 [10/21/1997]
In 3rd grade my son is learning how to add in bases
other than 10.
Ancient Math Symbols [09/07/1997]
subtraction
multiplication
division
fractions/decimals
Definitions
Geometry
2-dimensional
circles
triangles/polygons
3D and higher
polyhedra
I need to know the numerals for 1,10 100, 1000 in
Arab, Samarian, Greek, Roman, and Hindu.
Base 2 Subtraction and Clock Arithmetic [01/26/2001]
We know that computers use the "2's complement"
method to do subtraction of base 2 numbers, and that
this method works every time, but we have no idea
why it works.
Base Number [10/07/1998]
What does base number mean?
Golden Ratio/
Fibonacci Sequence
Composite Numbers [1/30/1996]
What are Composite Numbers?
History/Biography
Converting Fractions to Decimals [01/08/1997]
How do you convert fractions to decimals? How do
you turn decimals into ratios?
Measurement
calendars/
dates/time
temperature
terms/units
Difference Between Zero and Nothing [12/12/1996]
What is the difference between zero and nothing?
Number Sense/
About Numbers
infinity
large numbers
place value
prime numbers
square roots
Explanation of Place Values [05/08/2000]
What is meant when we say that as you progress from
the units place to the tens place to the hundreds place,
the value is increasing ten times the number on its
right?
Projects
Puzzles
Word Problems
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...
Multiplying by 0 [03/09/2001]
Why, when multiplying any number by 0, do you get
0?
Numbers between 0 and 9999 [7/15/1996]
How many whole numbers are there between 0 and
9999?
Numbers: Cardinal, Ordinal, Nominal? [10/25/1999]
Which group of numbers - cardinal, ordinal or
nominal - does "time" fit into? Are there other types
of numbers as well?
Perfect Numbers [08/14/1997]
What is the highest perfect number that has been
found? How many perfect numbers are there? What
are they?
Perfect Numbers - Basics, History [11/3/1996]
What is the next perfect number after 28?
Pi in Real Life [7/1/1996]
We have just covered circumference of circles and pi.
The children asked how this concept is used in real
life and who pi is named after.
Pi, Irrational Numbers [12/29/1994]
What is Pi and how does it work? What are rational
numbers and what are irrational numbers? How do
they work?
Plotting Coordinates on a Graph [07/02/1999]
How can I solve a problem like 3+(-2) = ? using a
number line, and how can I plot coordinates like (4,3) on an X-Y graph?
Prime Numbers vs. Prime Factors [01/13/1997]
What is the difference between a prime number and a
prime factor?
Properties of Real Numbers [05/20/1997]
What are the associative, the commutative, and the
zero product properties?
Rational and Irrational Numbers [2/2/1996]
What is the difference between rational and irrational
numbers?
Real and Other Numbers [08/29/2001]
What is a real number? What are the different kinds of
real numbers? Are there any more numbers besides
real numbers?
Repeating Decimals [5/31/1996]
I claim that 0.9 repeating is equal to 1...
Rounding to Specific Number of Significant Figures
[05/30/2003]
How do I round to five significant figures?
Rules for Significant Figures and Decimal Places
[03/23/1999]
Accurate measurement: What are significant digits?
When do we use them? Why?
Russian Peasant Method of Multiplication [10/07/1998]
I understand the 'Russian peasant' method of
multiplication, but not why it works.
Scientific Notation: Exponents [8/29/1996]
What do you call 0.000000000000000000000002?
Signs: Rules, Number Line [07/13/2001]
What is (-) - (+) = ? or (+) + (-) = ?
Subdividing Numbers, Number Line [12/20/1994]
I know about negative numbers and positive numbers
but are there any other numbers? What is a number
line?
Triangular Numbers [11/15/1995]
Second and third graders ask why 1 is a triangular
number.
Using Parentheses [11/16/1998]
Can you explain how to use parentheses to tell the
order of operations?
Venn Diagram of Our Number System [12/13/2002]
I don't know how to include complex numbers that
consist of a real part and an imaginary part. Can you
please diagram this for me?
What is i? [12/15/1995]
I heard about i being an imaginary number. Can you
please tell me what i really means?
What is Log? [2/26/1995]
What is 4 to the half power, and what is log?
Why does PEMDAS work? [7/9/1996]
Why does the PEMDAS (Parentheses, Exponents,
Multiplication, Division, Addition, Subtraction) order
of operations really work?
Why Do We Round? [12/18/2002]
What's the whole point of rounding?
Working with Integers [01/12/1999]
Could you explain how to divide, multiply, add, and
subtract integers?
Writing Commas in Numbers [07/11/2003]
Is it true that in France where we in America use
decimals in math, they use commas, and where we
use commas they use decimals?
0.999... and Infinity [09/17/2003]
How does x = 0.9999... forever turn into x = 1?
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