Question

my book has wrong answers in back of book. Would someone please help me check my answers?
Given a wheel with divided into 10 equal portions, numbers 1-10 on it, 5 of the numbers are red, 5 of the numbers are green.
What is P(4 or 7)?
I got 1/10 for the 4 and 1/10 for the 7. Then 1/10 + 1/10 = 2/10 or 1/5.
Because P(A orB) = P(A) + P(B).
My book says the answer is 4/5.
There are a series of problems, all with the wrong answers.
2) P(even or odd) :
P(even) = 5/10 since there are 5 even numbers on the wheel (2,4,6,8,10) = 1/2
P(odd) = 1/2 since there are 5 odd numbers on the wheel.

Answer 1

you are right, assuming they have equal area, \(P(4 or 7)=\frac{2}{10}=.2\)

Answer 2

it is not generally the case that the probability of A or B is the probability of A plus the probability of B though, that is only true if A and B are disjoint

Answer 3

i think that in your book it will be P(4 or 7)' if not then ur answer is absolutely correct:)

Answer 4

The answers at the back of the book are probably mistyped. The following is the next answer 4/5 - for the P( even or odd)/ I got 5/10 for even and 5/10 for odd. I do not see how they could get 4/5

Answer 5

@trailrunner47 don't go to the answers
believe in urself and solve:)

Answer 6

thanks! :D I try to check my own work before I turn things in. This time, I am unsure, so I am working the problems then checking my answers. Since the back of the book cannot be trusted, is there a web page or something anyone knows of where I can practice just straight up probabilities to see if I am getting it?

Answer 7

if you stuck anywhere go to the site wolfamalpha.com you will get answer:)