Math (probability)
posted by Maria .
Three members of a 12 person singing group are going to be chosen to sing a song in their coming concert.
A) how many different groups containing 3 people can be chosen from the 12 members of the singing group?
B) what Is the probability that mike and Jo will both be in the selected group?

b. three choices
?MJ
?JM
J?M
JM?
MJ?
M?J so there are six ways to get it, so probability is 6*(1/12*1/11*10/10)
a. 3!/12!9! 
oops a. 12!/(3!9!)=12*11*10/6=11*10*2
check that