We get many questions about classifying shapes, from both elementary and high school students (or their parents or teachers). They often have trouble with the very idea of classifying items by applying definitions, and also with the fact that definitions can vary, both between everyday and technical usages, and from one textbook to another.
(New Question of the Week) From time to time a student will ask for help understanding what he reads in his textbook. This often requires some back-and-forth as we try to understand both what the textbook is saying in its context (without having a copy of it to look at), and how the student is …
(Archive Question of the Week) Although high school and up probably constitute the majority of our questions, I always enjoy answering younger children. For today’s look at the archives, I thought I’d look at two such questions, both from 1999, and very memorable. The first is almost certainly the youngest “patient” we’ve ever had, and …
In a class on symbolic logic, students are taught the truth tables that define the “logical connectives” ∧ (and), ∨ (or), ¬ (not), and → (if … then). Everything makes sense until they are told that if p is false, then is true whether or not q is true. How can we say that “If pigs fly, then 2 is …
(Archive Question of the Week) Recently I discussed the definition of the median of a data set, pointing out how it needs refinements that are not often discussed. In searching for questions in our archive on that topic, I ran across a discussion of an opposite issue: the breadth of the general term “average”, which …
We frequently get questions about how to round; so many different issues arise that I won’t try to fit them all into one post. Children have trouble learning how to do it, and sometimes their parents are surprised to find that they are being taught a different way than they learned. There are several common …
(Archive question of the week) For Wednesdays, I plan to find a single interesting question from the past and discuss it. One of the things I’ve enjoyed about Ask Dr. Math is getting questions I’d never have thought of on my own, but which lead to some fascinating ideas. Here is an old favorite from …
From time to time we get questions about finding the median in statistics. Some are entirely routine; but the three I want to discuss today take us gradually deeper into a morass of ambiguity. A recurring theme of my experience in Ask Dr. Math has been that definitions are not always what they seem – …
Last time, we discussed how you know whether to add or multiply (or something else) in compound probability problems (like finding the probability that you will flip heads and roll an even number). But as I’ve said before, it’s often easier to remember a formula if you know why it is what it is. I’ll …
Last time, I talked about students’ difficulties carrying out divisions that involve a zero, which reminded me of another issue that sounds almost the same, but is quite different: division of a number by zero. Students often either forget the rule they were taught, or they don’t believe the rule, or they just wonder about …