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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.
 Pentagon Puzzle [09/18/2002]

Write the numbers 1 through 10 so each side of the pentagon has a sum
of 14.
 Percentage of Votes Cast [06/03/2003]

If you have two percentages, say 25% and 50%, can you do a percent
change between the two?
 Perfect Numbers [9/15/1996]

What is a "perfect number"?
 Pi's Last Digit [7/20/1996]

I know pi is a nonterminating decimal, but if there were a last digit
wouldn't the last digit be a 0?
 Placement of Commas in Writing Numbers [10/22/2003]

Why is the ones period named for the ones place value and why is the
thousands period named for the thousands place? Why is there not a
hundreds period?
 Precise Numbers [10/18/2001]

A precise number occurs when its proper divisors multiplied together
equal the number: 6 is a precise number because 1*2*3 = 6. Is there
another name or formula?
 Prefixes in Math [08/21/2001]

What are the prefixes for 7, 8, 9, and 10?
 Prime and Composite Numbers, Sieve of Eratosthenes [01/28/1997]

I need a list of all prime numbers and all composite numbers up to 50.
 Primes and Repeating Unit Numbers [12/09/1998]

How do you prove this statement: For every prime number there exists a
repeated unit number that is a multiple of that prime.
 Problem Solving and Mental Process [10/03/2002]

Two numbers add up to 19. The difference between the two numbers is 3.
What are the numbers?
 Proof: 2 = 1? [10/03/1997]

a = b is factored to a^2 = ab by multiplying both sides by a...
 Proof that 1 + 1 = 1? [09/04/1997]

Can you shed any light on this subject?
 Properties, Defined and Illustrated [10/10/2001]

I need a page of information on the commutative, associative, and
F.O.I.L. properties.
 Rational Numbers and Square Roots [10/07/1998]

Our teacher told us to find all the rational numbers we could containing
a sqrt symbol...
 The Real Number System in a Venn Diagram [09/08/1998]

How do you construct a Venn diagram that illustrates the real number
system?
 Reverse Polish Notation in Calculators [09/17/2005]

An introduction to "reverse Polish notation" and the terms "stack",
"push", and "pop" in that context.
 Roman Numerals [11/13/1997]

What are three ways Roman numerals are used today?
 Roman Numerals on Clocks [06/04/2001]

Is the Roman numeral on a clock written as IV, or IIII?
 Rounding to the Nearest Multiple of 5 [01/08/2005]

How do you round to the nearest 5? Would 27 round down to 25 while 28
would round up to 30?
 Rounding to the Nearest Tenth [8/29/1998]

Would 6.96 be 7.0 or 6.9?
 Saying Numbers Out Loud [03/06/2002]

I have recently been told that the use of "and" is incorrect. Is it "one
hundred one" or "one hundred and one"?
 Scientific Notation [09/16/1997]

I don't understand how you get the answer: 5x10 to the 3rd power = 5,000;
5x10 to the 3rd power = 5,000.
 Scientific Notation of Zero [09/09/2002]

What is the scientic notation of zero?
 Short Word Form [10/15/2002]

How is 474,136 written in short word form vs. standard form?
 Significant Digits [09/07/1998]

What are significant digits?
 Significant Digits and Irrational Numbers [09/24/2005]

How can you determine the signifigant digits of a nonterminating or
irrational number like pi?
 Significant Digits and Zero [05/19/1999]

When are zeros significant and when are they not significant?
 The Size of Infinity [09/03/1998]

What is infinity times 2? Can we measure infinity?
 Sizes of Infinities [01/31/1997]

How can you prove that one infinity is larger than another?
 Smallest 5Digit Number [02/05/2002]

My dad says the smallest 5digit number is 00000, but my teacher says it
is 10000. The dictionary says that zero is a digit. What's the right
answer?
 Spaces and the Number Line [02/26/2003]

If you say, 'How many degrees are there between 2 and 4?' would you
count the 0 degrees and answer 7 degrees or would you not count the
nought and answer 6 degrees?
 Square Numbers End in 0 1 4 5 6 9 [10/15/2002]

Why do all square numbers end in 0 1 4 5 6 9?
 Teaching Children Other Bases [02/20/2002]

Why teach children number systems other than the base 10 number system?
 Teaching Elementary Concepts [04/04/1997]

How can I teach rational counting, prime and composite numbers, and
square roots at a gradeschool level?
 Three Consecutive Natural Numbers [09/17/2001]

Why is it that the product of any three consecutive natural numbers is
always divisible by six?
 Trick for Numbers Divisible by 3 or 9 [02/24/1998]

Proof of a trick for numbers that are divisible by 3 or 9.
 Trilogy, Tetralogy... [05/28/2003]

Why isn't there a numbering system for groups like trilogies?
 Use and Meaning of 'And' in Naming Decimals [12/01/2004]

Can you please tell me what the word "and" means in the word form of a
decimal number?
 Use of Plural with Decimal Numbers [02/27/2002]

What are the rules for 1.0001, 1.1, 1.5 or 1.999 ? Should we write
1.0001, 1.1, 1.5, 1.999 point or 1.0001, 1.1, 1.5, 1.999 points ?
Differences between plurals in English and French.
 Using Integers [01/05/1999]

I need some reallife examples of integers to show my students that they
need to be able to use them in math class.
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