Khan Academy on Operations with Logarithms

Print Lesson


SWBAT to perform basic operations with logarithms and deepen their understanding of the laws of exponents

Big Idea

The laws of logarithms are simply a reflection of the laws of exponents.

Assessment Overview

10 minutes

These logarithmic modules are challenging because they heavy on notation. The word logarithm in itself scares most students. Here we are getting them some brief exposure to the concept. If nothing else, they will be easier to process the logarithmic content in high school. There are only 3 modules dealing with logarithms on Khan academy (although that is sure to expand). But students enjoy trying this new material (in many cases they have never even heard of a logarithm).

This module is the toughest to work with because it requires a mastery of the laws of exponents. Although I can't stress enough how rewarding it is for the students who get this far. For those who don't, they really enjoy mastering other topics from the unit.


The Assessment

40 minutes

The structure of the site is overwhelming to many students. To simplify the process, I have them log in to Khan Academy and then open a second tab and go straight to this link to get started today:

The guidelines for today are as follows:

  1. Finish the module until you reach "mastery." We encourage you at least 10 problems in a row. 
  2. As you work, write the questions and answers in your notebook.
  3. When you are finished, annotate your notes and explain some general observations you made as you worked. Identify the laws you used to solve each problem. 
  4. Create solve and explain a challenge problem that would fit nicely in each module.
  5. Write several numbers in exponential and logarithmic form. Explain how they are talking about the same numbers but from different perspectives.

I usually ask for part 5 in email and ask for very detailed explanations. Since all students have set me up as a coach I can easily monitor their progress after class. 

Assessment Review

10 minutes

I finish this assessment by reviewing questions with the class. I log into Khan Academy and project for the whole class to see. I popcorn around the room and ask students to solve and explain. For each question I get at least 2 algorithms, since students love to hear other strategies. I have noticed that many students use one strategy throughout all the problems and are usually so tired of it by the end that they crave a more efficient strategy. I wait until the end to share all strategies because I believe that process of struggling helps them process the importance of a more efficient strategy. If we just shared at the start, I think many students would blindly plug in the more efficient strategy without understanding why or how it is efficient.