SOLUTION: A math test has two problems. The first was solved by 70% of the students. The second was solved by 60%. Every student solved at least one of the problems. Nine students solved bot

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Question 182840: A math test has two problems. The first was solved by 70% of the students. The second was solved by 60%. Every student solved at least one of the problems. Nine students solved both problems. How many students took the test?
Answer by tvandenberg(45) About Me  (Show Source):
You can put this solution on YOUR website!
T = total number of student
X = number of students that solved second problem
Y = number of students that solved second problem
X / T = 0.70 --> X = 0.7 T
Y / T = 0.60 --> Y = 0.6 T
X + Y - 9 = T (since 9 students are in both X and Y)
0.7 T + 0.6 Y - 9 = T
0.3T = 9
T = 9 / 0.3 --> T = 30