# Calculating a ratio from a ratio pattern

I am having difficulty with the following problem

A computer chip manufacturer expects the ratio of number of defective chips to the number of chips in all future shipments to equal corresponding ratio for shipments S1,S2,S3 and S4 combined as shown in the table. What is the number of defective chips for a shipment of $60,000$ chips. (Ans=20). Any suggestions on how I could solve this problem?

I believe I am suppose to find S5 for $60,000$ which follows the ratio pattern. So I am doing the following

$16000$x =$60,000\times4$ so I get x=$15$ which is incorrect

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Oh, I didn't notice "combined". Ignore my previous comment. (edit: also, Google reveals it's a GMAT preparation question or something. E.g. see discussion here) –  user2468 Aug 29 '12 at 4:17