Answers

2016-04-24T00:48:25+05:30
X = proportionality coefficient
7x = pages of core section
2x = pages of advanced section

7x + 2x = 450
9x = 450
x = 50

7x = 7 × 50 = 350 pages of core 
2x = 2 × 50 = 100 pages of advanced

Check:
350:100 = 7:2  
350 + 100 = 450
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