anonymous
  • anonymous
Permutations/Combinations: A coin is tossed 20 times and the heads and tails sequence is recorded. From among all the possible sequences of heads and tails, how many have exactly seven heads?
Precalculus
  • Stacey Warren - Expert brainly.com
Hey! We 've verified this expert answer for you, click below to unlock the details :)
SOLVED
At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga. Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus. Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
katieb
  • katieb
I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!
anonymous
  • anonymous
it's just a combination: 20 choose 7 = 20C7\[\left(\begin{matrix}20 \\7 \end{matrix}\right)\] \[\frac{ 20! }{ (20-7)!7! }\] \[\frac{ 20! }{ 13! 7! }\] = 77,520
anonymous
  • anonymous
Oh, i understand it a bit better now. I put 40 instead of 20 because I thought it flipped 20 times and there are 2 heads..and multiply...it doesn't really make sense. Thanks for your hlep!
anonymous
  • anonymous
Remember this equation. \[\left(\begin{matrix}n \\ r\end{matrix}\right)\] or \[_{n} C _{r}\] Formula: \[\frac{ n! }{ r!(n-r)! }\]

Looking for something else?

Not the answer you are looking for? Search for more explanations.

More answers

anonymous
  • anonymous
also, does "different" mean a permutation?
anonymous
  • anonymous
different combinations?
anonymous
  • anonymous
like for example, How many DIFFERENT license plates consist of five symbols, either digits or letters? Would that be a permutation?
anonymous
  • anonymous
differrent means number of combinations.
anonymous
  • anonymous
Permutation is used to find the different combinations.
anonymous
  • anonymous
in general try to think of permutations as being used when order matters and combinations when order doesn't the license plate example is a permutation because you have a choice of symbols for each ordered position: ex.: 3 letters then 3 numbers --> # of possibles = 26*26*26*10*10*10 the standard example for combinations is for choosing committee members i.e. a committee of Peter and Mary is no different than a one of Mary and Peter; a permutation would doubly count this. that why combinations have another factor in the denominator to divide by to correct for this. perm. = n!/(n-r)! and combin. = n!/((n-r)!*r!) if the license plate was a combination then ABC123 would be no different then B21CA3 or any other arrangement of the characters

Looking for something else?

Not the answer you are looking for? Search for more explanations.