SOLUTION: a book seller buys 120 volumes of a certain series of books. he sells some at the published price of Rs. 18 each & disposes of the remainder during a cleaning sale at Rs. 12 each.

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Question 917307: a book seller buys 120 volumes of a certain series of books. he sells some at the published price of Rs. 18 each & disposes of the remainder during a cleaning sale at Rs. 12 each. if his total recipts are Rs. 1920. find how many volumes were sold at each price.please help me
Answer by KMST(5398) About Me  (Show Source):
You can put this solution on YOUR website!
DEFINING A VARIABLE TO START:
x= number of books sold at Rs. 18 each, which makes
120-x= number of books sold at Rs. 12 each.

REASONING:
So,
18x= money (in Rs.) received from the sale of x books at Rs. 18 each;
12%28120-x%29= money (in Rs.) received from the sale of 120-x books at Rs. 12 each,
and 18x%2B12%28120-x%29=1920= total receipts (in Rs.).
The equation to solve is 18x%2B12%28120-x%29=1920

SOLVING THE EQUATION:
18x%2B12%28120-x%29=1920
18x%2B12%2A120-12x=1920
18x%2B1440-12x=1920
18x-12x%2B1440=1920
%2818-12%29x%2B1440=1920
6x%2B1440=1920
6x=1920-1440
6x=480
x=480%2F6
highlight%28x=80%29
120-x=120-80
highlight%28120-x=40%29
highlight%2880%29 volumes were sold at Rs. 18 each,
and the remaining highlight%2840%29 volumes were sold at Rs. 12 each.