A) given a set of seven distinct positive integers, prove that there is a pair whose sum or whose difference is a multiple of 10. b) consider a square whose side has length one. suppose we select five points from this square. prove that there are two points whose distance is at most v2/2.

21/58.

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the revenue of the fitness center, y, is the product of two factors: the number of members and the fee paid by each member. there are 320 members now, but number of members goes down by 10 for each $5 increase in fees, so if x is the number of $5 price increases then members is equal to (320 - 10x). since the fee is currently $45, and the fee increases by $5 for every price bump x, the fee is given by (45 + 5x). so, revenue y is given by y = (320 - 10x)(45 + 5x).

the answer is c hope this