# Algebra

posted by on .

1)A bookshelf holds 4 mysteries, 3 biograpghies, 1 book of poetry, and 2 reference books. If a book is selected at random from the shelf, find the probability that the book selected is a biography or reference book.

A)1/2
B)1/6
C)5/6
D)3/50
I chose A

5 bio/reference/10 total books
1/2

2)Find the standard deviation of the data set to the nearest tenth. (21,13,18,16,13,35,12,8,15)

A)16.8
B)7.8
C)7.3
D)5.7
I chose C

mean = 21+13+18+16+13+35+12+8+15/9
16.8

variance = (21-16.8)^2 = 17.64...did that with the rest and added them to get sqrt 53.7

standard deviation = sqrt 53.7
= 7.3

3)Find the exact value of sin165
A)(sqrt6) - (sqrt2)/4
B)(sqrt6) + (sqrt2)/4
C)(sqrt2) - (sqrt6)/4
D)(sqrt of sqrt6 - sqrt2)/4
I chose A

(in D, there is a sqrt over both the sqrt6 and sqrt2

If I have it wrong can you explain how to do these types of problems b/c what I do is just take the sqrt of 6, subtract that from the sqrt of 2 and then divide by 4. I always end up with the same answer when I get the value of sin165 when I type it in my calculator

• Algebra - ,

For question one use:

P( A or B) = P(A) + P(B) - P(A and B)

The rule for OR takes into account those values that may get counted more than once when the probability is determined.

Let P = probability
Let A = biographies
Let B = reference book

Can you finish?

• Algebra - ,

No. why would I not just take the number of bio and ref. and divide by the total number of books?

• Algebra - ,

since P(A and B) from blueridge's formula is zero, you are right, total is 5
so prob. = 5/10 = 1/2