Probability

Question 1

Probability

Answer 1

• P=1; sure

- P=0; impossible (ie. P=0/5(heads/tails))

Question 2

Multiplicative Law

Answer 2

• a & b occurring (ie. two heads=0.5x0.x5=0.25)

Question 3

Probability (EG I)

Answer 3

• Cot death=1/1303 (P=0.000767); affluent and 26+ mom=1/8500 (P=0.000117); two affluent cot deaths=0.000117x0.000117=0.0000000136 (1 in 73 million)
• Siblings of cot deaths=10x more likely do also die cot death than average, so: cot death + sibling cot death=0.000767x(0.000767x10)=0.0000059 (1 in 170000 ie. 4 UK annual cases)

Question 4

Combination Rule

Answer 4

• CNr=N!/r!(N-r)!
• picking r out of N
• !=factorial operation (ie. 4!=4x3x2x1=24)

Question 5

Sample

Answer 5

• people being tested

Question 6

Population

Answer 6

• set of theoretically testable people

Question 7

Relativism

Answer 7

• compared summary stats (ie. mean) are equally true

Question 8

Realism

Answer 8

• one sum stat is better description of truth

Question 9

Probability (EG II)

Answer 9

o	Prob of 2 kids in a class having same bday?
o	N=30(group); r=2(pairs of bdays)
o	CR= CNr=N!/r!(N-r)!
o	30x29x28…/2!(30-2=28x27x26…)=(cancel from 28x…) 30x29/2=435
o	1/365(0.003)=ESTIMATE P of a pair of kids having same bday; them NOT having same bday=1-0.003=0.997x435ML=0.27 (no shared bdays only if no pairs share bday); 1-0.27=0.73=ACTUAL P of a pair sharing bday