AAPL wrote:Official Guide

If x books cost $5 each and y books cost $8 each, then the average (arithmetic mean) cost, in dollars per book, is equal to

A. \(\frac{5x+8y}{x+y}\)

B. \(\frac{5x+8y}{xy}\)

C. \(\frac{5x+8y}{13}\)

D. \(\frac{40xy}{x+y}\)

E. \(\frac{40xy}{13}\)

OA A

Cost of x book = 5*x = $5x;
Cost of y book = 8*y = $8y

Total cost of (x + y) books = $(5x + 8y)

Thus, average (arithmetic mean) cost, in dollars per book = (5x + 8y)/(x + y)

The correct answer: A

Hope this helps!

-Jay
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AAPL wrote:Official Guide

If x books cost $5 each and y books cost $8 each, then the average (arithmetic mean) cost, in dollars per book, is equal to

A. \(\frac{5x+8y}{x+y}\)

B. \(\frac{5x+8y}{xy}\)

C. \(\frac{5x+8y}{13}\)

D. \(\frac{40xy}{x+y}\)

E. \(\frac{40xy}{13}\)

OA A

Using the weighted average formula, we see that the average cost, in dollars per book, is:

(5x + 8y)/(x + y)

Answer: A

AAPL wrote:Official Guide

If x books cost $5 each and y books cost $8 each, then the average (arithmetic mean) cost, in dollars per book, is equal to

A. \(\frac{5x+8y}{x+y}\)

B. \(\frac{5x+8y}{xy}\)

C. \(\frac{5x+8y}{13}\)

D. \(\frac{40xy}{x+y}\)

E. \(\frac{40xy}{13}\)

OA A

Average cost per book = (TOTAL cost of all books)/(total number of books)

GIVEN: x books cost $5 each and y books cost $8 each
Cost of x books at $5 apiece = 5x
Cost of y books at $8 apiece = 8y
TOTAL cost of all books = 5x + 8y

TOTAL number of books = x + y

Average cost per book = (5x + 8y)/(x + y)

Answer: A

Cheers,
Brent