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← Unfrosted Cake - Visualizing Algebra

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Showing Revision 3 created 05/25/2016 by Udacity Robot.

  1. Let's try our hand at another unfrosted cake problem. If 1/6 of a cake is
  2. frosted with strawberry icing and 3/8 is frosted with blueberry icing, what
  3. fraction of cake is not frosted? To set up this problem, let's give ourselves a
  4. picture of what's going on. Here are two rectangular cakes and I have 1/6 of it
  5. frosted in strawberry icing. For this other cake, I'm going to frost 3/8 of it
  6. in blueberry icing. Notice I've split up the cake into 8 equal parts and I have
  7. 3 of those 8 frosted or 3/8. I'm not working with two cakes though, I'm working
  8. with one cake. So, let's visualize these two cakes on one. I'm going to show
  9. that here. So, notice I have 1/6 of the cake frosted in strawberry icing and 3/8
  10. of it frosted in blueberry icing. And we're trying to figure out what fraction
  11. is not frosted. The chocolate part. To set up this problem, we know we're going
  12. to start with one whole cake. Then, I need to subtract off 1/6 of the cake and
  13. 3/8 of the cake. So, I have 1 minus 1/6 minus 3/8. I can compare sixth to
  14. eighths right now, they are different size pieces so I can't just subtract these
  15. numbers. I need to get a common denominator, just like we did when adding
  16. fractions. So, let's try this with a quiz and see if we can remember how to find
  17. the common denominator. What do you think the common denominator would be for
  18. these fractions? Remember, you can list the multiples or use the factor tree.
  19. You don't have to worry about the one when finding the common denominator. This
  20. is because we can change the 1 into 2/2, 3/3, 12/12, or even a 107/107. All of
  21. these numbers are still equal to one. So, what's the common denominator for
  22. these fractions? You can put your answers in this box here. Remember, to find
  23. the common demominator, you can list the multiples or use the factor tree.