Is Zero Positive or Negative? Even or Odd?
Last week we looked at some basics about zero; now let’s look at whether zero is positive or negative, and then at the topic of the recent comment that triggered this series: whether zero is even or odd.
Arithmetic
Is Zero Really a Number?
A recent comment on the site raised questions about zero, beyond what we have discussed in the past about division by zero. Here we’ll look at basic questions about whether zero is actually a number at all, and then about multiplication by zero, which confuses a lot of people.
A Hen and a Half …
Last week, we looked at problems involving some number of people making some number of things in some amount of time. In a classic twist on this problem, we’ll now examine several variants starting with “If a hen and a half can lay an egg and a half …”. Can we make sense of half-eggs …
How Many A’s Can Make This Many B’s in This Much Time?
A popular kind of word problem tells us how many people (or cats, or hens, …) it takes to make some number of houses (or kill some number of mice, or lay some number of eggs) in some amount of time, and then asks us to fill in one of the blanks for a different …
How Many A’s Can Make This Many B’s in This Much Time? Read More »
Prime Factorization of a Number (Advanced)
Last time we looked at basic methods for finding the prime factorization of a number. Here we will look at some special techniques for large numbers, demonstrating them for not-too-large numbers. This takes us a step beyond previous tests that told us whether a number was composite, without actually factoring them.
Prime Factorization of a Number (Basics)
I’ll close this series on prime numbers by looking at how to find the prime factorization of a number, starting with the most basic ideas applicable to relatively small numbers, and then (next week) looking at some advanced methods for larger numbers.
Prime Numbers: Checking for a Prime (Part 2)
Last time we saw how to test small or medium sized numbers to see if they are prime, including details on the elementary Trial Division method, and introduced the most popular test for larger numbers, the Fermat test. Here we’ll review Fermat, and then go beyond. This is not for the faint-hearted! (I myself am …
Prime Numbers: Checking for a Prime (Part 1)
Last time we looked at how to efficiently make a list of prime numbers. But if you want to check a single large number to see if it is a prime, you don’t want to have to make a list of all primes up to that number. That’s today’s subject, where we’ll start with Trial …
Prime Numbers: Making a List
We’ve looked at what prime numbers are, and how the concept extends (or doesn’t) to 0, 1, and negative integers. The next question many students have is, how can I make a list of prime numbers (or write a computer program to do so)? We’ll learn about the Sieve of Eratosthenes, and list all the …
Prime Numbers: What About Negatives?
We’ve looked at the basic idea of primes, then at where 0 and 1 fit in. But what about negative integers? Can they be prime? If so, how does that affect the definition? And can you factorize a negative number if you don’t have negative primes?