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Safe Cracking

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skips
62
questions

Act One

• Dan Meyer

September 30, 2013

How long would it take to do what he did?

• 1.

What's a number you know is too high?

• 2.

What's a number you know is too low?

Act Two

• 3.

What information is important here?

• Teacher note
It seems like there are three important quantities here:

-- How long it takes him to write down one four-number combo.

-- How long it takes him to test one four-number combo.

-- How long it takes him to cross off one four-number combo.

You can have students collect their own data by timing the video and by seeing how fast it takes them to write down / cross off a few four-digit numbers.

Then you need to know what the final combination is. A close look at the video reveals "8020," but feel free to let your students make that determination.

Act Three

• Teacher note
So he writes down numbers 0000-9999. (Seems like a waste of time. What if the combo was "0000?")

He tests out numbers 0000-8020.

I assume:

-- Write a four-digit number down: 1 second.

-- Try it out and cross it off: 4 second.

Total time to write them down: 1 sec/number * (9999 - 0 + 1) numbers = 10,000 seconds.

Total time to try them out and cross them off: 4 sec/number * (8020 - 0 + 1) numbers = 32,084 seconds.

Total is 42,084 seconds or 701 minutes or 11.68 hours, which is a lot less time than I would have thought. Assuming he could do that for a couple hours per night without going crazy, and he'd be done in a week!

Sequel