* New MEMBER here - Discrete Math help *Prev TopicNext Topic

• mathNewbie

  

  United States
  Member #4,779
  May 24, 2004
  5 Posts
  Offline
  May 25, 2004, 8:37 am

  ▲▼
  Ok guys. A lot of co
• rdarmand

  

  United States
  Member #674
  September 4, 2002
  50 Posts
  Offline
  May 25, 2004, 12:50 pm

  ▲▼

  Hi, mathNewbie,

  That's the diagram I used.

  If you want to use Win D's approach, just assign the value "x" to subset g. Then: in d write "70-x"; in e write "50-x"; in f write "45-x.'

  Then ...

  You know that Circle 1 = 285 = a + d + f + g. So, a = 285 - (d + f + g). Since d = 70-x; f = 45-x; g = x, substituted these values for d, f & g, then simplify: a = 285 - [(70-x) + (45-x) + x] = 170 + x. Use the same approach to get b = 75 + x & c = 20 + x.

  Now, since you know that the sum of all seven subsets is 450 ...

  a + b + c + d + e + f + g = 450; (170+x) + (75+x) + (20+x) + (70-x) + (50-x) + (45-x) + x = 450; x = 20.

  Plug in "20" for x everywhere, and you know everything.

  The difference between Win D's approach and mine is simply the number of unknown variables used. His approach is more linear (PC), mine is more holistic (Mac). Comes out the same.

  I would guess that your teacher wants you to realize two things in the course of solving this problem: first, how to convert the "story problem" into a "math problem"; second, to understand why 70 = d+g, rather than just d. That will trip some people up, wait and see.

  Where n is equal to the number of tickets bought, the odds of winning in the MegaMillions lottery is given by 1 - [(1 - 0.023399196957)^n]
• mathNewbie

  

  United States
  Member #4,779
  May 24, 2004
  5 Posts
  Offline
  May 25, 2004, 12:52 pm

  ▲▼
  Yep. Thanks rdarmond