Question number

3.5 Probability & Conditional Probability - Conditional probability formula
0:00
Number of High School Students Who
Completed Summer Internships
High schoolYear
20082009201020112012
Foothill8780757670
Valley4454657682
Total131134140152152

The table above shows the number of students from two different high schools who completed summer internships in each of five years. No student attended both schools. Of the students who completed a summer internship in 2010, which of the following represents the fraction of students who were from Valley High School?

A.

10 over 140

B.

65 over 140

C.

75 over 140

D.

65 over 75

Number of High School Students Who Completed Summer Internships High school Year 2008 2009 2010 2011

Easy-difficulty · SAT Math · Probability & Conditional Probability — Conditional probability formula. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

Choice B is correct. According to the table, 140 students from the two high schools completed summer internships in 2010. Of these, 65 were from Valley High School. Therefore, of the students who completed summer internships in 2010, the fraction 65 over 140 represents the fraction who were from Valley High School.

Choice A is incorrect. This is the difference between the numbers of students from the two high schools who completed internships in 2010 divided by the total number of students from the two schools who completed internships that year. Choice C is incorrect. This is the fraction of students from Foothill High School who completed internships out of all the students who completed internships in 2010. Choice D is incorrect. This is the number of students from Valley High School who completed internships in 2010 divided by the number of students from Foothill High School who completed internships in 2010.