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

Selected answers to common questions:
    Place value questions.
    Rounding numbers.
    Scientific notation.
    Significant figures/digits.



Significant Digits and Irrational Numbers [09/24/2005]
How can you determine the signifigant digits of a non-terminating or irrational number like pi?

Significant Digits and Zero [05/19/1999]
When are zeros significant and when are they not significant?

Significant Digits in Measurement [08/13/2001]
I understand that there are rules to determine the significant digits in measurement, but aren't all digits significant, especially zeros for place value?

Significant Digits in Numbers Written in Scientific Notation [06/20/2005]
A discussion between Dr. Peterson and a student who is struggling with how to determine significant digits in general and with regard to numbers in scientific notation in particular.

Significant Figures [02/25/1999]
Why does 62.3 * 5.7 = 360 and not 355?

Significant Figures in 36 2/3 [11/06/2001]
How many significant figures are there in the area "36 2/3 Acres"?

Smallest 5-Digit Number [02/05/2002]
My dad says the smallest 5-digit number is 00000, but my teacher says it is 10000. The dictionary says that zero is a digit. What's the right answer?

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?

Subtracting and Borrowing in a Column [09/05/2002]
A student borrowed in a column as follows: 6.9 - 7.92, to get -2.98. Why won't borrowing work with this number?

Subtracting Mixed Fractions With Borrowing [01/08/2004]
Two methods for subtracting mixed fractions involving borrowing because the fraction being subtracted is larger than the other one. For example, 5 3/8 - 10 6/8.

Subtracting with Mixed Units [02/10/2009]
How would you subtract 1 ton, 12 lb, 6 oz from 4 tons?

Truncating [01/19/2002]
What does truncating mean?

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?

Using Hyphens to Indicate Place Value [08/30/2004]
What is the difference between "five hundred thousandths" and "five hundred-thousandths"?

What is a Number Base? [04/19/2003]
The base eight number 7n3 is equal to the base 7 number 1n35. What digit does n stand for?

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 the Decimal Point Moves when Multiplying by 10 [02/11/2005]
I am trying to explain why when you multiply a number by 10 you move the decimal point over one place to the right, and one place to the left when you divide by 10.

Working in Base 7 [08/02/2007]
How do I add, subtract, multiply and divide in base 7?

Working Up to Counting Up [09/25/2003]
My daughter wants to learn how to make change by counting up.

Writing Decimals from Words [10/05/1998]
Given a decimal written in words, how do you turn it into a decimal? In other words, how do you turn the words into numbers?

Writing Numbers in Words [09/15/1997]
Write each number in words: 1) 73.78007 2) 2.900087 (3) 34.4939.

Zeros after the Decimal Point [09/17/2001]
I have a group of students who just can't comprehend my explanation of how 3.70 is equivalent to 3.7 or 3.700 or 3.7000.

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