SOLUTION: C(10,r) =120. What is r? Please explain how you get r. Thanks

Algebra ->  Probability-and-statistics -> SOLUTION: C(10,r) =120. What is r? Please explain how you get r. Thanks      Log On


   

Question 1064626: C(10,r) =120. What is r?
Please explain how you get r. Thanks
Found 2 solutions by Fombitz, math_helper:
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Make a chart in EXCEL.
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Answer by math_helper(2461) About Me  (Show Source):
You can put this solution on YOUR website!
Since the numbers are small, I'd use trial-and-error:
C(10,5) = +10%21%2F%285%21%2A5%21%29+ = +10%2A9%2A8%2A7%2A6+%2F+%285%2A4%2A3%2A2%29+=+252+
C(10,6) = +10%21%2F%286%21%2A4%21%29+ = +10%2A9%2A8%2A7+%2F+%284%2A3%2A2%29+=+210+
C(10,7) = +10%21%2F%287%21%2A3%21%29+ = ++10%2A9%2A8+%2F+%283%2A2%29+=+120+
So C(10,7) satisfies the equation, so r=7 works… but note that C(10,7) = C(10,10-7) = C(10,3) so r=3 is also a solution.
Solutions are +highlight%28r=3%29+ and +highlight%28r=7%29+
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