OCR MEI S3 2012 January — Question 2

Exam BoardOCR MEI
ModuleS3 (Statistics 3)
Year2012
SessionJanuary
TopicLinear combinations of normal random variables
TypeDirect comparison of two variables

2 In a particular chain of supermarkets, one brand of pasta shapes is sold in small packets and large packets. Small packets have a mean weight of 505 g and a standard deviation of 11 g . Large packets have a mean weight of 1005 g and a standard deviation of 17 g . It is assumed that the weights of packets are Normally distributed and are independent of each other.
  1. Find the probability that a randomly chosen large packet weighs between 995 g and 1020 g .
  2. Find the probability that the weights of two randomly chosen small packets differ by less than 25 g .
  3. Find the probability that the total weight of two randomly chosen small packets exceeds the weight of a randomly chosen large packet.
  4. Find the probability that the weight of one randomly chosen small packet exceeds half the weight of a randomly chosen large packet by at least 5 g .
  5. A different brand of pasta shapes is sold in packets of which the weights are assumed to be Normally distributed with standard deviation 14 g . A random sample of 20 packets of this pasta is found to have a mean weight of 246 g . Find a \(95 \%\) confidence interval for the population mean weight of these packets.