Prob. Qns HELP!!!!! (1 Viewer)

[poowee]

In a gambling game, a computer wille take a random 13 numbers from the integers 1 to 40 inclusive. before this opccurs you are invited to chose 2 numbers, hoping your computer will match them amoungst its 13.

1) Show prob. of having both ur numbers matched is o.1

2) Find prob. that the computer will match:
a) niether of ur numbers
b) only one of ur numbers


3) In a succession of 7 games, find, as decimals the prob that both ur numbers will be matched:
a) exacatly once
b) at least once


CAN SOMEONE DO THIS AND EXPLAIN THE ANSWER

 

[freaking_out]

btw, where did u get this question from?

 

[ND]

1) The prob of having 1 number in the 13 drawn is 13/40, the prob of having both drawn is (13/40)^2=~0.1

2a) Similarly, the prob of having neither drawn is ((40-13)/40)^2 = (27/40)^2
b) Either two of the numbers can be matched here P(match, no match) = 13/40*27/40, P(no match, match) = 27/40*13/40. Now either of these can happen so you add them together.

3) For these use the binomial probability formula. For b), use the fact that P(at least 1 match) = 1 - P(no match).

 

[LadyMoon]

Actually ND i think you are wrong:
for the first one:
given that order doesnt matter....

You pick up 2 out of 40
there fore 40C2=780

it being the TWO in comp's 13 is 13C2=78

Therefore chances are 78/780=0.1

(it working on the others...)

 

[freaking_out]

whats with the spamming, ND?

 

[Fosweb]

database error?

 

[freaking_out]

Originally posted by Fosweb
database error?

lol or "ND" error.

 

[ND]

Originally posted by LadyMoon
Actually ND i think you are wrong:
for the first one:
given that order doesnt matter....

You pick up 2 out of 40
there fore 40C2=780

it being the TWO in comp's 13 is 13C2=78

Therefore chances are 78/780=0.1

(it working on the others...)

Yeh you're probably right.. i've said it many times and i'll say it again, i cannot do probability.

 

[ND]

Originally posted by freaking_out
whats with the spamming, ND?

All fixed.

 

[LadyMoon]

Yeah permb and combs is logic....damn (i hate logic) unlike the rest of 3unit maths which invloves Mr. Newton and Calculus!

Yay! go integration

 

[freaking_out]

Originally posted by ND
...i've said it many times and i'll say it again, i cannot do probability.

i wouldn't mind that, if i was a superbrain at every other topic.

btw, how did u get so smart at maths ND?

 

[ND]

I think you're exaggerating a bit there freaking_out.
There are others on this forum who are much better than i am.

LadyMoon, while i agree with your solution, i can't find the error in my logic, would you mind pointing it out?

 

[freaking_out]

Originally posted by ND
I think you're exaggerating a bit there freaking_out.
There are others on this forum who are much better than i am.

LadyMoon, while i agree with your solution, i can't find the error in my logic, would you mind pointing it out?

lol, na i wasn't saying u were the best (since u can't do probability. (not that i could or anything))...but yeah, ur still very smart at maths, so i just wanted to know ur secret (is it in the food u eat)?

 

[ND]

Originally posted by freaking_out
(is it in the food u eat)?

Shhh, don't tell everyone.

 

[LadyMoon]

Becuase the poster hasnt speicified whether the computer (or the player) can choose the same numbers twice, i'm assuming it (both player and comp) cant.

So instead of having (13/40)^2
i have 13/40*12/39=1/10 which is the same as the combinations i put up earlier!!
hope it hepled

but if the computer and the player can chhose the same numbers twice then...you'll be right!

 

[freaking_out]

Originally posted by ND
Shhh, don't tell everyone.

do u eat textbooks??

 

[LadyMoon]

Becuase the poster hasnt speicified whether the computer (or the player) can choose the same numbers twice, i'm assuming it (both player and comp) cant.

So instead of having (13/40)^2
i have 13/40*12/39=1/10 which is the same as the combinations i put up earlier!!
hope it hepled

but if the computer and the player can chhose the same numbers twice then...you'll be right!

 

[ND]

Ah i see, the thought that the numbers couldn't be chosen twice didn't even cross my mind. The question should've specified.

 

[ND]

Originally posted by freaking_out
do u eat textbooks??

That'd be quite an expensive diet.