homework question statistics

[davidh]

At “True North Adventure” there are 26 travel guides, 7 whom have first aid training. If 12 guides are chosen at random to go on an arctic expedition.

total possibilities is 26c12 = 9657700

A The probability that at least 2 of those chosen to go have first aid training is

B The probability that exactly 4 of those chosen to go have first aid training is

 

[Romsek]

Hypergeometric Multinomial Distribution

You have two groups, those with first aid training and those w/o.

 

[pka]

At “True North Adventure” there are 26 travel guides, 7 whom have first aid training. If 12 guides are chosen at random to go on an arctic expedition.
total possibilities is 26c12 = 9657700 CORRECT
A The probability that at least 2 of those chosen to go have first aid training is
B The probability that exactly 4 of those chosen to go have first aid training is

The probability of no one trained or exactly one trained \(=\dfrac{\dbinom{7}{0}\cdot\dbinom{19}{12}+\dbinom{7}{1}\cdot\dbinom{19}{11}}{\dbinom{26}{12}}\)
Now you have the answer to part A. We expect that you will post an exclamation why? as as your solution for part B.