ddsshin

10+ Year Member
Dec 6, 2006
211
0
Status
Dental Student
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??
 
OP
D

ddsshin

10+ Year Member
Dec 6, 2006
211
0
Status
Dental Student
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

Senior Member
10+ Year Member
7+ Year Member
Jun 30, 2005
2,780
2
Status
Pre-Dental
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.
 
OP
D

ddsshin

10+ Year Member
Dec 6, 2006
211
0
Status
Dental Student
if 3 cards selected randomly from a deck, what is prob of 3 cards are black?
 

Streetwolf

Ultra Senior Member
10+ Year Member
7+ Year Member
Oct 25, 2006
1,801
6
NJ
Status
Dentist
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.