Question
The average number of books of Biology, Chemistry and
Physics in a book shop is 360. Biology books are 180 more than the average number of Chemistry and Physics books. The number of Physics books is 180 less than the average number of Biology and Chemistry books. What is the number of chemistry books in the shop?Solution
: Let the number of biology, chemistry and physics books be B, C and P. B+C+P =360×3=1080 B+C+P=1080   … (1) Biology books =180+Average number of (C and P) B=180+(C+P)/2 2B=360+C+P 2B-C-P=360     … (2) Physics books =Average of (B+C)/2 -180 P=B+C)/2 -180 2P=B+C-360 B+C-2P=360    … (3) Adding Equation (1) and (3) and subtracting (2) ... (B+C+P) + B+C-2P -2B+C+P=1080+360-360 3C=1080 C=360.
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