对第五年数据进行检测.
Carry out a test on the 5th year's data.
第一步：
利用第四年的最佳拟合线（Tt=0.56X+25.6）进行计算第五年的Tt值
Step1:
Use the 4th year's best-fit line （Tt=0.56X+25.6）to work out the value of the 5th year's (Tt).
第二步：
将第五年的实际销售量与第五年的预测销售量进行对比.
Step2:
Comparethe 5th year's actual sales to the 5th year's forecast sales.
第三步：
根据公式来计算第五年的MAE以及MSE的值.
Step3:
Workout the 5th year's MAE and MSE by using the formula.
第四步：
通过计算其自由度为11和显著性水平为5%时的卡方值为19.68.
Step4:
Through calculation, when the degree of freedom is 11, the significant level is 5% and
the Chi-square value would be 19.68