# Math

posted by .

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

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 -

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 -

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 -

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 -

Add up all the grades that aren't B's. Then put that over the total amount of grades.

• Math -

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 -

Don't give up, you're right.... almost!

What Jen showed you to do was
P(not B), which equals 0.8

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.