Question

In USA Today (Sept. 5, 1996), the results of a survey involving the use of sleepwear while traveling were listed as follows: Male Female Total Underwear 0.220 0.024 0.244 Nightgown 0.002 0.180 0.182 Nothing 0.160 0.018 0.178 Pajamas 0.102 0.073 0.175 T-shirt 0.046 0.088 0.134 Other 0.084 0.003 0.087 (a) What is the probability that a traveler is a female who sleeps in the nude? (b) What is the probability that a traveler is male? (c) Assuming the traveler is male, what is the probability that he sleeps in pajamas? (d) What is the probability that a traveler is male if the traveler sleeps in pajamas or a T-shirt?

Answer 1

Answers:

a) 0.018.

b) 0.614.

c) 0.166.

d) 0.479

Explanations:

1) Table

----------------------Male ----------- Female ---------- Total

Underwear ----- 0.220 ---------- 0.024 ---------- 0.244

Nightgown ----- 0.002 ---------- 0.180 ------------ 0.182

Nothing --------- 0.160 ----------- 0.018 ------------ 0.178

Pajamas --------- 0.102 ---------- 0.073 ----------- 0.175

T-shirt ------------ 0.046 --------- 0.088 ------------ 0.134

Other --------------0.084 --------- 0.003 ------------ 0.087

2) Check that it is a table of relative frequencies:

total = 0.244 + 0.182 + 0.178 + 0.175 + 0.134 + 0.087 = 1 ⇒ indeed this is a table of relative frequencies.

That means that each data is a probabiilty.

3) Soluitions:

(a) What is the probability that a traveler is a female who sleeps in the nothing?

relative frequency of females that use nothing = 0.018

(b) What is the probability that a traveler is male?

Probability that a traveler is a male = relative frequency of males = 0.220 + 0.002 + 0.160 + 0.102 + 0.046 + 0.084 = 0.614

(c) Assuming the traveler is male, what is the probability that he sleeps in pajamas?

It is the relative frequency of the males that sleep in pajamas divided by the relative frequency of males = 0.102 / 0.614 = 0.166

(d) What is the probability that a traveler is male if the traveler sleeps in pajamas or a T-shirt?

It is the relative frequency of males that sleep in pajamas plus that of the males that sleep in T-shirt, divided the total relative frequency of travelers that sleep in pajamas or T-shirt

i) relative frequency of males that sleeps in pajamas plus that of the males that sleeps in T-shirt = 0.102 + 0.046 = 0.148

ii) relative frequency of travelers that sleep in pajamas or T-shirt = 0.102 + 0.046 + 0.073 + 0.088 = 0.309

iii) quotient = 0.148 / 0.309 = 0.479

Answer 2

A) 0.018/1= 0.018
b) Probability of Male in survey is 0.614. Therefore the asked probability is
     0.614/1=0.614.
c) Now we are dividing with probability that person is Male.
    0.102/0.614=0.166.
d)Probability that person sleeps in either T-shirt or pajamas is  0.175+0.134=0.309
   Probability that male sleeps in pajamas or T-shirt
is  0.102+0.046=0.148
Final answer is:
0.148/0.166=0.479