Let the big restaurant be X and the small restaurant be Y. According to the meaning of the question: (1) x+2y =1680 (2) 2x+y = 2280 (1) times 2: (3)2X+4Y=Y=360 and then (3) Substituting Y=360 into (1) gives X+720= 1680, so X=960.
Therefore, opening seven restaurants together =5X+2Y=4800+720=5520, and because 5520 is greater than 5300, it is ok.
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