Question

	Smoke	Do Not Smoke
Junior	52	148
Senior	110	70
TOTAL	162	218

1. If a student from the survey is randomly selected, the probability that a junior/senior smokes is __________. (answer in decimal form rounded to two decimal places).

Is this a conditional probability? (yes, no).

2. If a student from the survey is randomly selected, the probability that a junior/senior does not smoke is_________. (answer in decimal form rounded to two decimal places).

Is this a conditional probability? (yes, no).

3. If a student from the survey is randomly selected, the probability that a student is junior, and smokes is ________. (answer in decimal form rounded to two decimal places).

Is this a conditional probability? (yes, no).

4. If a senior student from the survey is randomly selected, the probability that the senior student smokes is______________. (answer in decimal form rounded to two decimal places).

Is this a conditional probability? (yes, no).

5. If a student who smokes is randomly selected, the probability that the student is junior is _________. (answer in decimal form rounded to two decimal places).

Is this a conditional probability? (yes, no).

Answer 1

The table is

	Smoke	Do not smoke	Total
Junior	52	148	200
Senior	110	70	180
Total	162	218	380

i) The probability that a junior/senior smokes is

= 162/380 = 0.426

This is not a conditional probability.

ii) The probability that a junior/senior doesn't smoke is

= 218/380 = 0.574

This is not a conditional probability.

iii) The probability that a student is junior and smokes

= 52/380 = 0.137

This is not a conditional probability

iv) The probability that the senior student smokes is

= 110/180 = 0.611

Yes, this is a conditional probability.

v) The probability that the student is junior, given that the student smokes is

= 52/162 = 0.321

Yes, this is a conditional probability.

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