Today is the last day of Amazon's Prime Day, this year stretched out to a four-day sales event. Adobe Analytics predicts that customers will have shelled out nearly $24-billion over Prime Day, some $9.6-billion more than last year. The biggest drivers behind the increase were expected to be school and office supplies. Momentum Commerce manages sales for some retailers on the platform and said sales were down more than 40-percent on the first day compared to last year, but was still projecting an overall growth in sales. Amazon, however, is rejecting those first day sales numbers, calling them "highly inaccurate."