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28. A survey conducted on Ianuary 30, 2003, for Wal-Mart reported that on average, peo- ple planned to spend $51 on the purchase of a Valentine's Day gift that year. A survey of 40 people aer Valentine's day in 2003 found they had spent an average of $64 with a standard deviation of $18. Test the hypothesis at the .05 level that the population mean expenditure on Valentine's day gifts in 2003 was higher than $51