Twelve is the first number with two pairs of factors (2 x 6 and 3 x 4). Primes, on the other hand, have no pairs of factors other than the trivial pair of one and the prime number itself. Considering that contrast, here’s an interesting fact about primes and the number 12. Add 12 to […]

# Archive | Divisibility

# How to tell if a Number is Divisible by 8

How to tell if 8 divides into a number. There is a simple test for this. This post explains this.

# How to See Why the Divisibility Trick for 3 Works

There’s a nifty trick for finding out if 3 divides evenly into a number. This little proof shows why the trick works.

# (Divisibility) Practice Makes Perfect

Practice problems for reducing fractions. Use divisibility tricks to reduce fractions.

# Divisibility by 7: Is there really a trick?

There’s a weird and interesting trick for divisibility by 7. This blog tells you how to do it. Sit back and be amazed.

# Divisibility by 6: How to find out if 6 divides in cleanly

Learning the rules of divisibility helps all students succeed at math. Learning the trick for 6 is really helpful because it is not easy to see if 6 goes in for most people. This trick makes it much easier to tell.

# Divisibility by 4 — Principles & Trick

It is not hard to find out if 4 goes into a number evenly. Here is a trick that shows you how to find out very quickly.

# Divisibility: Find out if 3 divides evenly into an integer

Learning the divisibility tricks speeds up mental math. How to know if 3 divides into a number evenly? This blog tells you how

# “Fraction Sandwich” Practice Problems: Dividing a Fraction by a Fraction (without choking!)

Last week I sent out a blog that helps students divide a fraction by a fraction. The technique is called the “Fraction Sandwich.” To help students “get the hang” of this technique, here are 10 practice problems for dividing one fraction by another.

# Multiplication Trick #3 — Multiply by 25 FAST!

Here’s a great way to help students get two for the price of one. First, they make connections between multiplication and a topic very dear to their hearts: money. That’s because the trick is for multiplying by 25, and in using this trick, you use the fact that four quarters make a dollar. Secondly, students […]