Ask Dr. Math

Elementary Archive

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

See also:
      Calendars/Dates/Time
      Temperature
      Terms/Units of Measurement

Selected answers to common questions:
    A million/billion seconds.
    Significant figures/digits.
    Unit conversions, unit cancellation.
    Using a protractor, reading a ruler.

---

Groups and Units: Multiply or Divide? [04/15/2003]

Changing units to other units.

Measurement: Precision vs. Accuracy [01/07/2003]

Using a metric ruler student A measured the length of an object to the nearest tenth (0.1) of a centimeter, while student D measured its length to the nearest centimeter. Which measurement is more accurate?

Reading a Ruler [09/18/1997]

I need to read a ruler, and I can't. Can you help me?

Unit Conversions: mph to fps [03/06/2003]

How can I find out how many feet per second I could travel driving 55 miles per hour?

What is a Significant Digit? [12/25/2001]

I came across a question asking for an answer with no more than "2 significant digits" - can you please explain what a significant digit is?

2 Square Feet vs. 2 Feet Square [11/22/1998]

What is the difference between 2 square feet and 2 feet square?

Accuracy in Measurement [01/09/2007]

I've heard that it's impossible to measure things exactly, and I don't understand that. How can our world be based on estimations?

Choosing a Unit of Measurement [05/06/2002]

What's the proper unit of measurement for measuring butterflies?

Complementary or Supplementary? [04/02/2001]

I keep getting complementary and supplementary mixed up. How can I remember which is which?

Converting Metric Measurements [11/03/2005]

I don't understand how to convert 50 millimeters into centimeters. Do I multiply 50 by 10 or divide it by 10? How do I decide?

Converting Millimeters to Inches and Back [03/14/2003]

I would like to see how to calculate without a chart.

Converting Volumes, Such As Cubic Inches To Cubic Feet [02/09/2004]

I would like to fill a sandbox with 3 inches of sand. The sandbox measures 25ft X 80ft. How much sand do I need to buy?

Explanation of Significant Figures [09/11/2007]

I'm confused about how to determine how many significant digits a given number has. Can you explain it?

Feet Per Second [02/22/2003]

Determine the velocity in a pipe in ft. per second... Where does the constant term in the formula come from?

Fraction or Decimal? [06/23/1998]

Which is more precise, a fraction or a decimal - for instance, 1/3 or 0.33?

Fundamental Idea of Division [03/24/2000]

My 8-year-old daughter had 12 bracelets which she arranged into 4 piles of 3. Did she divide 12 by 3 or by 4?

How Many Blocks in a Mile? [11/24/2005]

How many city blocks are there in a mile?

Inches and Feet and Miles, Oh My! [04/14/2008]

Why are English measures inconsistent in conversions? The metric system works in the meter and power of tens, but English units are kind of crazy (1 ft = 12 in, 3 ft = 1 yd, 1 mi = 1760 yd or 5280 ft, etc.).

Learning Fractions in the Metric System [11/27/2003]

Since the metric system doesn't use fractions, are math students in metric countries able to skip fractions and work on more useful things?

Measurement and Comparison [04/30/1999]

Why is comparison the key to measurement?

Measuring a Puddle [09/05/2002]

How many different ways can you measure a puddle?

Metric and Standard Rulers [04/20/2001]

In the United States we only use a customary (standard) ruler, and in other parts of the world they use the metric side. Why do we just use the standard side?

Metric vs. Standard System [08/19/2001]

Compare and contrast the advantages and disadvantages of the metric system and the standard system using weights and measures.

Numbers and Numerals [11/20/1998]

What is the difference between numbers and numerals?

Pennies in a Mile [04/23/1999]

How many pennies are there in a mile?

Reaction Time: Softball, Baseball [04/26/2003]

A baseball pitcher throws at 90mph from 60 feet, and a softball pitcher throws at 60mph from 40 ft. How can I measure reaction time for the batters?

Reading a Ruler II [11/08/2000]

What do the little lines on a ruler stand for?

Reading a Ruler III [03/03/2005]

I am looking for simple, basic instructions to teach a child how to read a ruler. I remember that we used to count the lines--where the line falls on the ruler is the top number of the fraction and how many lines in between 0 to 1 inch represents the bottom number (the whole). Is this correct?

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 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.

Some Conversions are Impossible [08/07/2006]

How do I convert 567 square inches to cubic inches?

Strategies for Solving Word Problems with Fractions and Units [08/02/2007]

On a road map with a scale of 1/4 inch per 10 miles, the highway from Waukee to Winterset is 1 3/8 inches long. How many miles long is this highway?

Subtracting with Mixed Units [02/10/2009]

How would you subtract 1 ton, 12 lb, 6 oz from 4 tons?

Teaching the Metric System [08/18/2000]

How can I teach my second grader about the metric system? I have no idea how to read a metric ruler or how to convert inches into the metric system or vice versa.

Using Scale Drawings [05/24/2002]

Use a scale drawing to determine the actual size of an object.

Which Grasshopper Wins the Race? [06/11/2003]

The larger grasshopper covers 10 inches per jump, while the smaller one covers 5 inches. The smaller grasshopper takes 2 jumps for every jump of the larger grasshopper. Which one wins, and why?

Page:  1