SOLUTION: At a school assembly there are 100 students in grade 9, 125 in grade 10, 225 in grade 11, and 170 in grade 12. Everyone at the assembly entered their name for a door prize. What is

Algebra ->  Probability-and-statistics -> SOLUTION: At a school assembly there are 100 students in grade 9, 125 in grade 10, 225 in grade 11, and 170 in grade 12. Everyone at the assembly entered their name for a door prize. What is      Log On


   

Question 1170633: At a school assembly there are 100 students in grade 9, 125 in grade 10, 225 in grade 11, and 170 in grade 12. Everyone at the assembly entered their name for a door prize. What is the probability that the prize will be won by,
a) a grade 11 or 12 student?
b) a grade 12 student, if all grade 11 students are disqualified from winning?
Thanks


Answer by math_tutor2020(3817) About Me  (Show Source):
You can put this solution on YOUR website!

Part (a)

There are 100+125+225+170 = 620 students total.

Of that total, 225+170 = 395 are in grades 11 or 12

Divide the values to get the fraction 395/620 = 79/124

Use your calculator to find that 79/124 = 0.6371

Exact Answer as a fraction = 79/124
Approximate Answer in decimal form = 0.6371
Approximate Answer in percent form = 63.71%

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Part (b)

Subtract off the 225 grade 11 students who are disqualified

The total goes from 620 to 620-225 = 395

Or you could add up the other grades that aren't grade 11
100+125+170 = 395

Divide the number of grade 12 students over the new total 395 to get 170/395 = 34/79 = 0.4304 = 43.04%

Exact Answer as a fraction = 34/79
Approximate Answer in decimal form = 0.4304
Approximate Answer in percent form = 43.04%