Abank is investigating ways to entice customers to charge more on their credit cards. (banks earn a fee from the merchant on each purchase, and hope to collect interest from the customers as well.) a bank selects a random group of customers who are told their "cash back" will increase from 1% to 2% for all charges above a certain dollar amount each month. of the 500 customers who were told the increase applied to charges above $1000 each month, the average increase in spending was $527 with standard deviation $225. of the 500 customers who were told the increase applied to charges above $2000 each month, the average increase in spending was $439 with standard deviation $189. when testing whether or not the increases in spending are different, the test is significant at alpha. gif =

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a. 5%.
b. 1%.
c. 0.5%