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I posted this earlier with a huge typo. Please do this question again if you can.

c.)in a stack of six cards, each card is labeled with a different integer 0 through 5. If two cards are selected at random w/o replacement, what is the probability that their sum will be THREE?

typo=i put 2 instead of 3..thanks for the other answers tho.

By anon2121 on Sunday, December 29, 2002 - 02:28 pm: Edit

There's 6!/(4!*2!) = 15 combinations of two cards that can be selected. The ones that will equal 3 are {0,3) and {1,2}. Therefore, the probability that the sum will be 3 is 2/15.

By 660M on Sunday, December 29, 2002 - 02:32 pm: Edit

YES!! I knew there was some weird system i wasnt aware of..bare with me, im only in algebra 2 (11th grade)... explain what these exclamation points mean and how you got 6!4! 2!

By 660M on Sunday, December 29, 2002 - 02:33 pm: Edit

note: i know how to find the !'s on my ti-83, so its not necessary that you go into a long explanation

By Brian on Sunday, December 29, 2002 - 02:58 pm: Edit

4! = 4 * 3 * 2 * 1

By Sabzevarian (Sabzevarian) on Sunday, December 29, 2002 - 03:16 pm: Edit

It is factorial notation. It's not that hard, but I'm not sure if or when you cover that in the US curriculum.

By Pat57575 (Pat57575) on Sunday, December 29, 2002 - 03:32 pm: Edit

660m, if you were wondering how anon got his answer, the number of combinations that are possible is n!/(r![n-r]!) where n is the total number of cards and r is the size of the groups they are being split into.

**note** in combinations order doesn't matter. {0,3} would be considered the same thing as {3,0}.

By 660M! on Sunday, December 29, 2002 - 05:02 pm: Edit

THANK YOU!!!! See, i wasnt aware of the formula, ok. Im so happy..this is actually making sense.
BTW, my calc has a whole row of buttons under "Probability". ! is one of them, does anyone know what the others do or if they would be useful for the SAT??

By vp on Monday, December 30, 2002 - 03:08 am: Edit

LOL....... 660M .... the '!' button is for factorial... its like 6!= 6*5*4*3*2*1...same way 5!= 5*4*3*2*1

ok another thing for probability...the formulae generally dont make sense..so just logic it out....dunno if u guys have conditional prb or baeyers formula/method.....so the one thing that always works...remmeber.....is logic