destroyer QR 64

[ddsshin]

there is 70% chance of rain each day for 3 days. what is prob it will rain 2 days out of 3 days?

--- can someone explain how to solve this??

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[ddsshin]

ok... i am not sure the difference between
n!/(n-r)! and n!/r! (n-r)! how are they used differently in QR section?

 

[joonkimdds]

You are asking the difference between permutation and combination.
permutation is the same award. Let's say the first 3 girls entering my room will get to have the same awards, that's permutation.

1st girl entering my room can stay 1 hr, 2nd girl can stay 30 min, 3rd girl can stay 1 min, this refers to 3 diff awards so this is combination.

 

[ddsshin]

if 3 cards selected randomly from a deck, what is prob of 3 cards are black?

 

[pez123]

there is 70% chance of rain each day for 3 days. what is prob it will rain 2 days out of 3 days?

--- can someone explain how to solve this??

This thread really helped me understand all the probability stuff. The answer to your question is towards the bottom.

http://forums.studentdoctor.net/showthread.php?t=541781

 

[Streetwolf]

You are asking the difference between permutation and combination.
permutation is the same award. Let's say the first 3 girls entering my room will get to have the same awards, that's permutation.

1st girl entering my room can stay 1 hr, 2nd girl can stay 30 min, 3rd girl can stay 1 min, this refers to 3 diff awards so this is combination.

You got those mixed up. Combo is order doesn't matter.