Question

A researcher is selecting lab rats for her experiment. She assigns each rat a number and picks numbers out of a hat while blindfolded. The pool of rats from which she is drawing participants is composed as follows: 23 male albino rats 21 male spotted rats 35 female albino rats 11 female spotted rat

If she reaches into her hat twice, what is the probability of choosing:

a. Two female albino rats?

b. A female spotted rat and a male albino rat?

c. A male albino rat and then either a female albino rat or a male spotted rat?

d. A female spotted rat and then either a male spotted rat or a female albino rat?

Answer 1

Answer)

Probability is given by favorable/total

23 male albino rats

21 male spotted rats

35 female albino rats

11 female spotted rats

Total = 23 + 21 + 35 + 11 = 90

A)

Two female albino rats

P(albino female) = 35/90

P(second female albino) = 34/89 {as after picking 1 total left would be 90-1 = 89, same for female albino}

P(both female albino) = {(35/90)*(34/89)} = 0.14856429463

B)

P(female spotted rat) = 11/90

P(male albino) = 23/89

Required probability is = (11/90)*(23/89) = 0.03158551810

C)

P(male albino rat) = 23/90

P(female albino or male spotted) = (35+21)/89

Required probability is (23/90)*(56/89) =

0.16079900124

D)

P(female spotted rat) = 11/90

P(male spotted or female albino) = (21+35)/(89)

Requiried probability is (11/90)*(56/89) = 0.07690387016