OG详解-OG6 数学1 Q10

Choice B is correct. It’s given that the shop’s inventory starts with 4,500 paper cups and that the manager estimates that 70 of these paper cups are used each day. Let x represent the number of days in which the estimated supply of paper cups will reach 1,700. The equation 4,500-70x = 1,700 represents this situation. Subtracting 4,500 from both sides of this equation yields -70x = -2,800. Dividing both sides of this equation by -70 yields x = 40. Therefore, based on this estimate, the supply of paper cups will reach 1,700 in 40 days.
Choice A is incorrect. After 20 days, the estimated supply of paper cups would be 4,500-70(20), or 3,100 cups, not 1,700 cups. Choice C is incorrect. After 60days, the estimated supply of paper cups would be 4,500-70(60), or 300 cups, not 1,700 cups. Choice D is incorrect. After 80 days, the estimated supply of paper cups would be 4,500-70(80), or -1,100 cups, which isn’t possible.