Derrick invested in certificates and bonds. the certificates paid 4% interest and the bonds paid 5%.the total investment was $1000 and the total amount you got was $48.50. how much did he invest in the certificates?

At the beginning of a call to the cable company, a message tells customers, "after you finish talking to our customer service representative, you will be asked to take a five-question survey about the level of service you recieved. it would be appreciated if you could stay on the line to answer the survey questions." what type of sampling is the cable company using?