Table:
Shipment, # of Defective Chips in Shpmt, Total #Chips in Shpmt
S1 2 5,000
S2 5 12,000
S3 6 18,000
S4 4 16,000

A computer chip manufacturer expects the ratio of the number of defective chips to the total number of chips in all future shipments to equal the corresponding ratio for shipments S1, S2, S3, and S4 combined, as shown in the table above. What’s the expected number of defective chips in a shipment of 60,000 chips?

Answer Choices:
14
20
22
24
25


Answer is 20

I don't understand how to solve this problem. I tried finding an average and then multiplying the average for 1,000 chips in a shipment by 60. The other thought I had was to combine sets of past shipments to make 60,000---for example, 5 shipments of S2 (5*12,000) makes a shipment of 60,000, so I figured the answer was 25 (5 defective chips of S2 * 5 times the shipments). What is the right approach to solve this problem? Thanks.