Question
The average number of books on Biology, Chemistry, and
Physics in a book shop is 300. Biology books are 150 more than the average number of Chemistry and Physics books. The number of Physics books is 150 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 =300×3=900 B+C+P=900     … (1) Biology books =150+Average number of (C and P) B=150+(C+P)/2 2B=300+C+P 2B-C-P=300     … (2) Physics books =Average of (B+C)/2 -150 P=B+C)/2 -150 2P=B+C-300 B+C-2P=300    … (3) Adding Equation (1) and (3) and subtracting (2) ... (B+C+P) + B+C-2P -2B+C+P=900+300-300 3C=900 C=300.
42, 54, 78, 114, 168, 222
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