Z-tests (known variance)

All Questions
A company packages white sugar from two farms $U$ and $V$ in 1 kg packets. Throughout the exercise, results should be rounded, if necessary, to the nearest thousandth.
  1. The company announces that $30\%$ of the packets of sugar bearing the label ``extra fine'' that it packages contain sugar from farm U. Before validating an order, a buyer wants to verify this announced proportion. He randomly selects 150 packets from the company's production of packets labeled ``extra fine''. Among these packets, 30 contain sugar from farm U. Does he have reason to question the company's announcement?
  2. The following year, the company declares that it has modified its production. The buyer wishes to estimate the new proportion of packets of sugar from farm U among the packets bearing the label ``extra fine''. He randomly selects 150 packets from the company's production of packets labeled ``extra fine''. Among these packets $42\%$ contain sugar from farm U. Give a confidence interval, at the $95\%$ confidence level, for the new proportion of packets labeled ``extra fine'' containing sugar from farm U.