Posted by **Shannon** on Sunday, December 5, 2010 at 10:02am.

If a grade was drawn at random from the data shown below, what is the probability that the grade is not a B?

Grade Frequency

A 2

B 8

C 11

D 2

F 1

I think it is 1 out of 5 or 4 but I am not sure? Please help :) Thank you much!

- Math -
**MathMate**, Sunday, December 5, 2010 at 10:04am
There are 5 possible outcomes, one of which is a B.

So what is P(B), and what is P(not B)?

Hint : P(B) and P(not B) have to add up to 1.

- Math -
**Shannon**, Sunday, December 5, 2010 at 10:10am
Oh ok I think I get it, so P(B)=0.5, 1/2,

and P(not B)=0.5,1/2???

Is that right?

- Math -
**MathMate**, Sunday, December 5, 2010 at 11:13am
Sorry, not really.

Figure out the probability of P(B) which is to get B out of 5 possible choices.

The rest would be easy to figure out.

- Math -
**Jen**, Sunday, December 5, 2010 at 1:20pm
Add up all the grades that aren't B's. Then put that over the total amount of grades.

- Math -
**Shannon**, Sunday, December 5, 2010 at 3:51pm
Ok so it would be P(B)=0.8, the probability that the grade is not a B.?

I hope this is right now, if it isn't I give up....lol !

- Math -
**MathMate**, Sunday, December 5, 2010 at 5:13pm
Don't give up, you're right.... almost!

What Jen showed you to do was

P(not B), which equals 0.8

("...grades that aren't B's...")

there is only one grade B, so it is 1/5, there are 4 grades that are not B, so

P(not B)=4/5=0.8

Sorry if it was too confusing, hope it's more clear now.

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