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 ration for shipments S1, S2, S3, and S4 combined, as shown in the table above. What is the expected number of defective chips in a shipment of 60,000 chips? 答案是20 这题是分别算上面的4个数 然后相加呢,还是分子分母分别加起来之后再相除呢??