5 pens cost as much as 7 pencils 21 pencil costs as much as 10 books 16 books cost as much as 9 boxe...........

Quantitative Aptitude (CDS) Ratio, Proportion

5 pens cost as much as 7 pencils, 21 pencil costs as much as 10 books, 16 books cost as much as 9 boxes, the cost of 1 box is equal to Rs. 82. What is the cost of 1 pen?

Rs.13

Rs.15

Rs. 12

Rs. 10

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Explanation:

x = 1pen , 5pen = 7pencil, 21pencil = 10 books, 16 books = 9boxes, 1box = Rs.32
16 books = 9×32
1book = 9×32/16 = 18
21pencil= 10×18
1pen = 10×18/21= 60/7
5pen = (7×10×6)/ 7 = 60/5
= Rs.12