The mean value of accounts received by a firm is thought to be 260. An auditor checks this by taking a sample of 20 accounts, which are found to have...

The mean value of accounts received by a firm is thought to be £260. An auditor checks this by taking a sample of 20 accounts, which are found to have a mean of £240 and standard deviation of £45. Use 5% significance level to test whether the original view is supported by the evidence of the sample.