1. Student government
a) Combinations of committes of 3 students
455
b) Probability of choosing Brett, Eric, and Jeff
2730
= 1/2730
c)
120
= 1/120
2. Snow days
# of snow days Probability
x P(X=x) x(PX=x) x² x²*P(X=x)
2 0.10 0.20 4 0.40
3 0.15 0.45 9 1.35
4 0.70 2.80 16 11.20
5 0.05 0.25 25 1.25
sum (μ): 3.70 sum: 14.20
a) E(X) snow days
E(X) = 2 0.10 + 3 0.15 + 4 0.70 + 5 0.05∙∙∙∙
E(X) or μ = 3.7
μ²= 13.69
b) Standard deviation of x
σ =
=
=
= 0.714142843
3. Plastic surgeon
Event A1 Patient books a surgery
Event A2 Patient doesn't book a surgery
Event B Patient refers a friend
P(A1) 0.8 [Probability that patient books after consulation]
P(A2) 0.2 [Probability that patient does not book after consulation]
P(B|A1) 0.7 [After patient books, probability that patient refers friend]
P(notB|A1) 0.3
[After patient books, probability that patient DOESN'T refer friend]
1-0.7= 0.3
4. Assumption school
Morristown (MT) 0.6
15C3 =
15C3 =
6C3 =
15!/3!12!=
(15∙14∙13∙12!)/(3∙2 ∙1∙12!)=
(15∙14∙13∙12!)/(3∙2 ∙1∙12!)=
2730/6=
15!/((15!−3!))=
15!/12!=
(15∙14∙13∙12!)/12!=
2730/1 =
6!/((6!−3!))=
6!/3!= (6∙5∙4∙3!)/3!=
2730/1 =
√(14.20
−(3.7))²
√(14.20
−13.69)
√0.51
