Three sisters purchased treats at a bake sale. The oldest sister spent $2.70 on brownies. The middle sister spent four times as much on cookies as the older sister spent on brownies. The youngest sister spent $3.68 less on a cake than the middle sister spent on cookies. How much did each sister spend?

An energy drink company claims that its product increases students' memory levels. to support its claims, the company issues advertisements claiming that 8 out of 10 people (chosen randomly from across the country) who tried their product reported improved memory. the missing component in this study is a .