SOLUTION: Hi Bob bought some books at an average cost of $23.85 each. He mistakenly bought a book for $48.90 instead of another book that cost $12.90. The average cost of the books that Bob

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Question 1176483: Hi
Bob bought some books at an average cost of $23.85 each. He mistakenly bought a book for $48.90 instead of another book that cost $12.90. The average cost of the books that Bob bought should have been $19.35. How many books did he buy. Thanks
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Bob bought some books at an average cost of $23.85 each.
He mistakenly bought a book for $48.90 instead of another book that cost $12.90.
The average cost of the books that Bob bought should have been $19.35.
How many books did he buy.
:
let n = number of books bought
let a = total amt spent on the books not given here
:
Two equations
%28%28a+%2B+48.90%29%29%2Fn = 23.85
and
%28%28a+%2B+12.90%29%29%2Fn = 19.35
:
multiply by n, we can use elimination here
a + 48.90 = 23.85n
a + 12.90 = 19.35n
---------------------Subtraction eliminates a
0 + 36 = 4.50n
n = 36/4.5
n = 8 books