The crisp new dollar bill that I have just taken from my wallet bears the serial number 24598176. It’s easy to tell that the number is exactly divisible by 2 but not by 5. Is it divisible by 3? by 4?

It’s easy to tell if a given whole number is divisible by 2. Just check whether the last digit is even. There are also simple rules to determine whether a number is ...

This article is a modified and updated version of one I wrote in—oddly enough—2008 and then updated for 2012. Barring a colossal asteroid impact or a Trump presidency, I’ll probably be around to do it ...

After multiplication, it is time to learn certain divisibility rules to ease our calculations. The basic rules for divisibility by 2, 3, 5, 9, 11 are fairly well known. So now we are going to learn ...

If you’ve ever had to buy hot dogs for a cookout, you might have found yourself solving a math problem involving least common multiples. Setting aside the age-old question of why hot dogs usually come ...