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# Lock Combinations of Knobs and Keys

Media Type:
Video

Running Time: 1m 49s
Size: 5.1 MB

or

Source: Cyberchase: "A Day At the Spa"

### Collection Developed by:

Collection Credits

### Collection Funded by:

Funding for the VITAL/Ready to Teach collection was secured through the United States Department of Education under the Ready to Teach Program.

In this video segment from Cyberchase, the CyberSquad must figure out the correct doorknob/key combination in order to open the door which stands between them and the Black Crystal. The CyberSquad has doorknobs in three different colors and keys in three different colors. After a few failed attempts, they decide to use a grid to help them keep track of the different combinations they have tried.

Connections

Everyday Math (2004)
Teacher Lesson Guide, pp. 564-575
Student Reference, pp.
Math Journal, pp. 221-225
Math Master, pp. 111-112, 321-322, 324

Investigations/Scott Foresman (2006)
(5th Grade) Between Never and Always
Investigation 1, Sessions 1-4, pp. 4-26

Teaching Tips

Here are some Frame, Focus and Follow-up suggestions for using this video in a math lesson.

What is Frame, Focus and Follow-up?

Frame: Let’s say you have a friend who really likes to coordinate her outfits. If she has three different color hats and two different color scarves, how many hat and scarf combinations does she have to choose from? How did you figure this out? Is there any opportunity to use multiplication to help you figure out the number of combinations?

Focus: In this video segment, you will watch Jackie and Matt as they try to find the correct doorknob/key combination to open a high security door. As they test some possible combinations, pay attention to what they do to make sure they try each combination without repeating or missing any possibilities.

Follow Up: How many combination possibilities did Jackie and Matt find? How did they use multiplication to help? When they laid out the knobs and keys Jackie said, “It’s like a grid of possibilities!" What did she mean?

Transcript

MATT: It didn't open!

JACKIE: Let me try a different combination. No luck.

MATT: Here's another combination! No dice. Wait! Didn't we already try that combo?

JACKIE: I'm not sure...I don't remember.

MATT: Time out! We need to keep track of each combination so we can tell which ones we've tried and which ones we haven't.

JACKIE: You're right! And we need a way to be sure we've tried them all. So... let's organize our choices.

MATT: Three knobs: orange, green, purple.

JACKIE: And to make a combination, we match a knob with a key...red...blue...yellow.

MATT: But that's only three combos. What happens if we lay them out like this?

JACKIE: Cool! Now it's like a grid of possibilities. This one is green knob plus blue key.

MATT: And this square is purple knob plus red key.

JACKIE: A square for every combination, and a combination in every square! I think we're onto something!

MATT: Three keys by three knobs makes nine squares, so we have nine different combinations to try.

JACKIE: The same as the number of knobs, three, multiplied by the number of keys, three!

MATT: I forgot which combinations we already tried. Let's start over and check off the combinations as we go.

JACKIE: The first combination is orange knob, red key. Wrong combination.

MATT: Next up: orange knob, blue key. Mark it! Nope. Let's try again. This is the last combination! It better work. Yes!

Standards

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