# Math Lesson Plan: Using Significant Digits

By chemteacher

Do you hear moans and whines when you tell your students to round their answers to significant digits? When you teach the subject do you get at least one student asking, "why do we have to learn this?" If this sounds like you, read on. I will give you a mini-lesson plan that will help...

## Michael Phelps by a fraction!

Start by having students watch this short you-tube video: Michael Phelps Wins!

Recap the event, highlighting the fact that Phelps won by only 0.01 seconds, one one-hundreth of a second.

Next, give the students the following instructions: Round each number to 1 significant digit. (Answers are in parenthesis.)

9999 (10,000)

999 (1,000)

99 (100)

9.9 (10)

0.99 (1)

0.099 (0.1)

If your students are anything like mine, some of them will round the last example to 0. The idea that the zero after the decimal but before an integer is just a place holder is difficult for some to understand. This is when you play the Michael Phelps card. Point out that he won the race by 0.01 seconds. If that zero after the decimal was considered significant, we'd have to round the amount of his victory off to 0.0, and that's no margin to win by.

Those placeholder zeros can confuse students. By giving them a real-life example to relate back to it will be easier for them to comprehend and remember.