请帮忙解释一下这道shl题目这道是shl官方网站上的例题，但是不太明白，希望有牛人指教，多谢图片请参考：http://w

请帮忙解释一下这道shl题目
这道是shl官方网站上的例题，但是不太明白，希望有牛人指教，多谢
图片请参考：
http://www.***.com/phasei/helpsection-phaseI/images-numerical/Buttons.gif
1. What percentage of the total 15mm button production was classed as sub-st
andard in September?
A 10.5% B 13% C 15% D 17.5% E 20% F 23.5% G 25%
H 27.5% I 28% J 30.5%
2. By how much did the total sales value of November's button production vary from October's?
A.8.50(Decrease) B.42.50(Decrease) C.85.00(Increase)
D.27.50(Decrease) E.No change
3. What was the loss in potential sales revenue attributable to the production of sub-standard (as opposed to standard) buttons over the 6 month period?
A.13.75 B.27.50 C.137.50 D.280.00 E.275.00