？3. 卖东西，half are sold at $29, mean=?
1) 1125 items are sold at $29
2) 40% sold at 39, 10% at 9
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[确认]B
没看懂什么意思！！那位高人帮指点指点啥意思呗！！作者: 自尊宝 时间: 2003-3-12 16:26
潜泳强书上的题吧，反正见过。
2） 50%，sold at 29; 40%,39;10%, 9
=> the mean =50%*29 + 40%*39 +10% * 9
OK.done.
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