Leonidas252
New member
- Joined
- Jun 17, 2014
- Messages
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Hello everybody. I have math exam tommorow and I'm having problems with more complicated exercices and with some exercices concerning dice rolls and marbles.
Example n.1.
We roll 7 times d6,what's possibility of getting:
a) exacly 3 aces(ones);
I think i found the answer to this one: P(A)= (3*5^4)/6^7 or 7*6*5*5^4)/6^7 is this right?
b) at least 3 aces;
c) at most 3 aces.
im having trouble applicating the 7 rolls. i know that if i would have rolled only 3 times the probability for a) would be (1/6)^3.
Example n.2.
We have 15 marbles in a box(7 white, 5 red and 3 black). What's the probability of getting 2 red marbles in the 2 cases:
a) we take 3 marbles out without putting them back in the box;
b) we take 3 marbles, putting each one back after making note of its colour.
In this one i belive there are involved combinatorics but im not entirely sure.
Example n.3.
There are 7 digits numbers that can be composed without any limits(repetition allowed),
how many numbers have in them two 2's, one 3, one 4 and three 5's. I think the answer to this one is 7! but i'd nonetheless like to get it confirmed.
Example n.4.
We have a deck of 32 cards. In how many ways can we draw 6 cards with:
a) exacly 1 ace;
b) at least 1 ace;
c) exacly 1 ace and 2 kings;
d) ace of spades and at least 1 card of clubs
e) 3 cards of one colour(hear,diamonds...), 2 of different colour and 1 of different colour.
In this one I'm kinda lost
I'm sorry for the abuse but it's really urgent and i don't have much time. Thanks for any contribution.
Example n.1.
We roll 7 times d6,what's possibility of getting:
a) exacly 3 aces(ones);
I think i found the answer to this one: P(A)= (3*5^4)/6^7 or 7*6*5*5^4)/6^7 is this right?
b) at least 3 aces;
c) at most 3 aces.
im having trouble applicating the 7 rolls. i know that if i would have rolled only 3 times the probability for a) would be (1/6)^3.
Example n.2.
We have 15 marbles in a box(7 white, 5 red and 3 black). What's the probability of getting 2 red marbles in the 2 cases:
a) we take 3 marbles out without putting them back in the box;
b) we take 3 marbles, putting each one back after making note of its colour.
In this one i belive there are involved combinatorics but im not entirely sure.
Example n.3.
There are 7 digits numbers that can be composed without any limits(repetition allowed),
how many numbers have in them two 2's, one 3, one 4 and three 5's. I think the answer to this one is 7! but i'd nonetheless like to get it confirmed.
Example n.4.
We have a deck of 32 cards. In how many ways can we draw 6 cards with:
a) exacly 1 ace;
b) at least 1 ace;
c) exacly 1 ace and 2 kings;
d) ace of spades and at least 1 card of clubs
e) 3 cards of one colour(hear,diamonds...), 2 of different colour and 1 of different colour.
In this one I'm kinda lost
I'm sorry for the abuse but it's really urgent and i don't have much time. Thanks for any contribution.
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