Ask Dr. Math Tour

The Dr. Math Archive is among the greatest benefits of the program. As we've answered questions we've saved the best of them, together with their answers, and have put them on the Math Forum Web site. The Archive currently contains over 3000 questions, and we're adding to it every month so that it is becoming a valuable resource for math information.

The questions are organized by level (Elementary, Middle School, High School, and College and Beyond) and by subject (Addition, History, Calculus, etc.). Students can browse or use the powerful searcher to look for questions by keyword. They may find new answers to old questions, or new questions that they have not yet considered.

Here we include a small sampling of the thousands of questions in the Dr. Math Archives.

Elementary School

Subtracting Big Numbers [Stanseski, 11/20/95]
What's 245715 - 105065 ?

Who Invented Decimals? [Beck, 11/8/94]
We are fifth grade students and one teacher. We would like to know who invented decimals.

Middle School

Height of Ripped Paper [Va, 11/17/95]
Rip a piece of 8 by 11 paper in half, then put that half over the other, then rip it again. What is the length (or how high, like 5 miles or something) when the paper is ripped 30 times?

Multiplying Negative by Negative [Spencer, 11/6/94]
I'm trying to make sense of these rules so that they'll be easier to memorize: Pos x Pos = Pos, makes sense. I've been doing it since 3rd grade. And I can even think of a situation. I get six birthday cards with $5 in each. Pos x Neg = Neg, I can think of a situation for this, too. I get four bills for $20 each so I'd owe money. But, Neg x Neg = Pos just doesn't make sense. Does it ever happen in real life? My teacher said that you could say it would be the opposite of Pos x Neg but that seems like cheating. It's not realistic.

High School

Complex Roots [Scott, 11/1/94]
We know it is possible to look at the graph of a polynomial and tell a great deal about its real roots by looking at the x-intercepts. What can be discovered about a polynomial's complex roots by looking at the graph? There seem to be some interesting "wiggles" at locations that appear to be related to the "average" of the complex pairs. It appears that the "wiggle" of these graphs is always influenced by the complex roots. What we are trying do is develop a graphing technique that will let us find the complex roots from the real graph. (Contributions by Profs. Conway and Maurer.)

Break a dowel to form a triangle [Chen, 3/8/95]
A wooden dowel is randomly broken in 2 places. What is the probability that the 3 resulting fragments can be used to form the sides of a triangle?

College and Beyond....

Analysis [, 11/29/94]
In analysis: If f:[0,1] is continuous. Show that there is an x in [0,1] such that f(x) = x. Problem #2: If A and B are open and closed sets respectively, of R^n, show B\A is closed and A\B is open.

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