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!
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.
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?
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.
Add up all the grades that aren't B's. Then put that over the total amount of grades.
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 !
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.
To find the probability that the grade drawn is not a B, we need to find the total number of grades (sum of all frequencies) and subtract the frequency of B from it.
Total number of grades = 2 + 8 + 11 + 2 + 1 = 24
Therefore, the probability of not getting a B is (Total number of grades - Frequency of B) / Total number of grades:
= (24 - 8) / 24
Simplifying, we have:
= 16 / 24
Reducing the fraction, we get:
= 2 / 3
So, the probability of the grade not being B is 2/3 or approximately 0.67.
Therefore, the correct answer is not 1 out of 5 or 4, but 2 out of 3, or 2/3.