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

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) (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%

================================================
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%

RELATED QUESTIONS
The students at King High School are in grades 9, 10, 11, and 12. Of all of the students, (answered by stanbon)

Jamey wanted to understand whether students at her school were in favor of an extended... (answered by jim_thompson5910)

Krissy wanted to understand whether grade level had any relationship to their opinion on... (answered by jim_thompson5910)

If there are 50 students in the class. 14 got A Grade 22 got B Grade 11... (answered by Boreal)

There are 150 students in grade 9. If 38% of the students are girls how many more... (answered by Boreal)

there are 6 boys to every 9 girls in the sixth grade. there is a total of 75 students in... (answered by ankor@dixie-net.com)

At a middle school, 38% of all seventh graders have taken swimming lessons. There are 250 (answered by mathybrain)

There are 152 students in 5th grade. 1/11 of the boys and 5 girls join a science club. In (answered by Theo,ankor@dixie-net.com,MathTherapy)

A team composed of two grade11 and two grade 10 students is to be sent to a debate... (answered by ikleyn)