Last August the XT chain of gasoline stations had a temporary sales promotion in effect. In the promotion , any customer who made a purchase of ten or more gallons of gasoline was entitled to a free car wash . For the month of August , XT experienced a ten percent increase in gasoline sales as compared to sales in August the previous year so evidently the promotion was successful as a means of boosting sales.
 In evaluating the argument, it would be most helpful to answer 'Are XT's gasoline sales in August usually significantly higher than one twelfth of XT's annual gasoline sales?'