Houses/workers/days problem (direct and inverse variation)

Today I want to feature a great video from a fellow blogger and Youtuber, Dave Marain. He solves this question, which at first can sound intimidating:

If 10 workers can build 3 houses in 60 days, how many workers are needed to build 5 houses in 40 days?

It sounds like you'd need algebra, proportions, inverse or direct variation, etc. And true, you could use those. But his method completely avoids all that and is based on setting up a simple TABLE, AND using common sense!


|  HOUSES  |  WORKERS  |  DAYS  |
----------------------------------
|    3     |    10     |  60    |
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|    1     |    10     |        |
----------------------------------
|    2     |    10     |        |
----------------------------------
|    5     |           |        |
----------------------------------


See the video below:




And here's a link to his other Youtube videos: www.youtube.com/user/MathNotationsVids.
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