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5a) 3/7
B) 1/3

## #2 Re: Help Me ! » More discrete mathematics questions » 2012-12-04 01:09:16

3) 4^n
4) 120!/20!60!40!

2) 2^40 (50,10)

## #4 Re: Help Me ! » More discrete mathematics questions » 2012-12-04 01:06:38

I worked through them all but am not sure if they're correct.
For question
1a) I have 70!
B) C(70,12)
C) C(35,8)*C(20,4)*C(15,0)
D) 35!*20!*15!

## #5 Re: Help Me ! » Help! Discrete mathematics » 2012-12-04 00:44:34

bobbym wrote:

Hi;

Post #5 contains all the answers you require.

I see the solutions but could you also post how you got to the solution?

## #6 Help Me ! » More discrete mathematics questions » 2012-12-04 00:42:49

Jhua4
Replies: 14

1) suppose you have 70 books (35 novels, 20 history books and 15 math books). Assume that all 70 books are different
A) in how many different ways can you put 70 books in a row on a shelf?
B) in how many different ways can you choose a set of 12 books to give to a friend?
C) in how many different ways can you choose a set of 4 history books and 8 novels to give to a friend?
D) in how many different ways can you put the 70 books in a row on a shelf if the novels are on the left, the math books are in the middle and the history books are on the right?

2) what is the coefficient of x^40 and y^10 in the expansion of (2x+y)^50?

3) give a simple expression for the value of the following sum (as a function of n):
C(n,0) + 3 * C(n,1) + 3^2 * C(n,2) +...+ 3^n-1 * C(n,n-1) + 3^n * C(n,n).

Your formula should not involve sums or combinatorial symbols like P(n,r) or C(n,r). Using the binomial theorem briefly justify why your answer is correct.

4) you have 20 pennies, 60 nickels and 40 dimes. Assume that the pennies, dimes and nickels are identical. In how many different ways can you put all the coins in a row?

5) assume we are using LaPlace's probability model, where all outcomes are equally likely. An urn contains 70 balls, of which 10 are red, 20 are blue and 40 are green. Let b be a randomly chosen ball.
A) what is p(b is not green)?
B) what is p(b is blue | b is not red)?

## #7 Re: Help Me ! » Help! Discrete mathematics » 2012-12-04 00:25:29

Sorry I meant the following:
The cards are identical and no envelope can be left empty

## #8 Re: Help Me ! » Help! Discrete mathematics » 2012-12-04 00:14:38

Could you explain how you got to that solution please? Thanks!

## #9 Re: Help Me ! » Help! Discrete mathematics » 2012-12-03 23:46:46

So what exactly is the correct answer for a)? Thanks!

## #10 Re: Help Me ! » Help! Discrete mathematics » 2012-12-03 23:31:02

We have learned the following formula for putting distinguishable objects into distinguishable boxes: n!/n1!n2!...nk!

So I'm a little confused as how to apply that formula to the question.

## #11 Help Me ! » Help! Discrete mathematics » 2012-12-03 23:15:31

Jhua4
Replies: 10

You have 25 cards, 15 distinguishable envelopes (i.e. envelopes are labeled 1,2,3...,15). You may put any non-negative number of cards into an envelope. In how many ways can you put the 25 cards if
a) the cards are distinguishable (e.g., if each has different message on it)
b) cards are identical
c) cards are identical and no card can be left empty

I can't figure out the answers for this problem. Help is much appreciated!:)