6.
某公司为确定下一年度投入某种产品的宣传费,需了解年宣传费\(x(\)单位:千元\()\)对年销售量\(y(\)单位:\(t)\)和年利润\(z(\)单位:千元\()\)的影响,对近\(8\)年的年宣传费\(x_{i}\)和年销售量\(y_{i}\)\((i=1,2,···,8)\)数据作了初步处理,得到下面的散点图及一些统计量的值.
\(\bar{x} \) | \(\bar{y} \) | \(\bar{w} \) | \(\sum\limits_{i=1}^{8}{{}}\) \((x_{i}- \) \(\bar{x} \) \()^{2}\) | \(\sum\limits_{i=1}^{8}{{}}\) \((w_{i}- \) \(\bar{w} \) \()^{2}\) | \(\sum\limits_{i=1}^{8}{{}}\) \((x_{i}- \) \(\bar{x} \) \()(y_{i}-\) \(\bar{y} \) \()\) | \(\sum\limits_{i=1}^{8}{{}}\) \((w_{i}- \) \(\bar{w} \) \()(y_{i}-\) \(\bar{y} \) \()\) |
\(46.6\) | \(563\) | \(6.8\) | \(289.8\) | \(1.6\) | \(1469\) | \(108.8\) |
表中\(w_{i}=\sqrt{{x}_{i}} \), ,\(\bar{w} \) \(=\dfrac{1}{8}\sum\limits_{i=1}^{8}{w}_{i} \)
\((\)Ⅰ\()\)根据散点图判断,\(y=a+bx\)与\(y=c+d\sqrt{x}\)哪一个适宜作为年销售量\(y\)关于年宣传费\(x\)的回归方程类型?\((\)给出判断即可,不必说明理由\()\)
\((\)Ⅱ\()\)根据\((\)Ⅰ\()\)的判断结果及表中数据,建立\(y\)关于\(x\)的回归方程;
\((\)Ⅲ\()\)以知这种产品的年利率\(z\)与\(x\)、\(y\)的关系为\(z=0.2y-x.\)根据\((\)Ⅱ\()\)的结果回答下列问题:
\((i)\) 年宣传费\(x=49\)时,年销售量及年利润的预报值是多少?
\((ii)\) 年宣传费\(x\)为何值时,年利率的预报值最大?
附:对于一组数据\((u_{1}\) \(v_{1})\),\((u_{2}\) \(v_{2})…….. (u_{n\;}\) \(v_{n})\),其回归线\(v=\alpha +\beta u\)的斜率和截距的最小二乘估计分别为:
\(\hat {β}= \dfrac{ \sum\nolimits_{i=1}^{n}({u}_{i}- \overset{¯}{u})({v}_{i}- \overset{¯}{v})}{ \sum\nolimits_{i=1}^{n}({u}_{i}- \overset{¯}{u}{)}^{2}},\hat {a}= \overset{¯}{v}-\hat {β} \overset{¯}{u} \)