SOLUTION: a small school bus contains 8 first graders and 10 second graders. if 2 children were ill, what is the probability that at least one of them is a second grader? thanks

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Question 326901: a small school bus contains 8 first graders and 10 second graders. if 2 children were ill, what is the probability that at least one of them is a second grader?
thanks
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Let's find the probability that both are first graders.
P(1st 1st)=8/18=4%2F9
P(2nd 1st)=7%2F17
P(2 1st)=%284%2F9%29%287%2F17%29=28%2F153
"At least 1 second grader" means "not both 1st graders".
P(both 1st)+P(not both 1st)=1
P(not both 1at)=1-28/153=125%2F153
P(at least 1 2nd)=125%2F153