SOLUTION: An owner of a fast food restaurant reported to corporate headquarters that the average bill paid by his customers in the last quarter was $6.20 and that the standard deviation was

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Question 133947: An owner of a fast food restaurant reported to corporate headquarters that the average bill paid by his customers in the last quarter was $6.20 and that the standard deviation was $1.90. Not knowing exactly what the effect would be, headquarters suddenly launched a nationwide promotional campaign featuring a large quantity discount for a multi-sandwich purchase. The stubs from the next 81 purchases at the owner�s franchise after the campaign was launched averaged $6.65.

Conduct the 5 step hypothesis test at a level of significance of 0.05 to determine if the promotion increased the average bill amount.
Answer by stanbon(75887) (Show Source):
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An owner of a fast food restaurant reported to corporate headquarters that the average bill paid by his customers in the last quarter was $6.20 and that the standard deviation was $1.90. Not knowing exactly what the effect would be, headquarters suddenly launched a nationwide promotional campaign featuring a large quantity discount for a multi-sandwich purchase. The stubs from the next 81 purchases at the owner�s franchise after the campaign was launched averaged $6.65.

Conduct the 5 step hypothesis test at a level of significance of 0.05 to determine if the promotion increased the average bill amount.
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Ho: mu(before)-mu(after)= 0
Ha: mu(before)-mu(after) < 0
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Critical value for alpha = 5%: t = -1.645
Test Statistic: t(6.20-6.65)/sqrt[(1.9^2/n1)+(s2^2/81)]= ?
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Comment: n1 is missing from the before data; s2 is missing from
the after data.
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Cheers,
Stan H.