The Comma Method for Reading Large Numbers

Once I developed this tip, my students quickly mastered how to read long numbers.

Take the example 165,247,873

I showed my students that within each comma, the numbers follow the standard hundreds-tens-ones protocol. The comma simply indicates whether you are dealing with millions, thousands or plain old units (the name some people give the hundreds-tens-ones group.)

Each three-digit group can be read as if it were just a hundred. Referring to our example number, you first say “One hundred sixty-five.” The comma signifies millions since you are in the third comma group from the right. Thus, you begin reading the number by saying “one hundred sixty-five MILLION.” (Capital letters added for emphasis—they’re very helpful for students.)

Then, you read the next three-digit group as if it were a hundred: “two hundred forty-seven” and then add the THOUSAND. (I point to the comma as I loudly say “THOUSAND.”

Last, read the last three-digit group as a regular number: “eight hundred seventy-three.”

Thus, your number is “one hundred sixty-five MILLION, two hundred forty-seven THOUSAND, eight hundred seventy-three.”

Once I taught my students this, they understood why each place is important. They had less trouble reading and writing numbers with a zero as a placeholder, such as 207,800. After all, you just read each three-digit group as a regular old hundred: “two hundred seven THOUSAND, eight hundred.”

Ironically, our math book teaches place value only to the ten thousands. I think that’s to save children from that horrifying extra place value that would take them to the hundred thousands. But when I taught to the hundred thousands and even hundred millions using this method, the confusion (for the most part) went away.

Posted in Academics,Math by Corey Green @ Nov 29, 2011


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