题库搜索>问题求解PS-13756
At a certain food stand, the price of each apple is ¢ 40 and the price of each orange is ¢ 60. Mary selects a total of 10 apples and oranges from the food stand, and the average (arithmetic mean) price of the 10 pieces of fruit is ¢ 56. How many oranges must Mary put back so that the average price of the pieces of fruit that she keeps is ¢ 52?
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设买苹果X个，橙子Y个。
X+Y=10.
（40X+60Y）/10=56
联立，求出X=2，Y=8。
再设要放回的橙子数量为a，【40*2+60*（8-a）】/10-a=52,a=5
虫0515
救命，陷阱！
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2021-10-18 20:38:02
jessica要超过720
要放回橙子，前提是苹果数量保持不变，所以不能和第一次拿时列一样的式子！！
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2019-09-14 21:44:27
wlcheer
这题出的好
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2019-04-04 16:03:47
266063ei回复wlcheer
是的呀！陷阱就在它让人以为放回去之后总数还是10
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2021-04-12 17:06:19
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