送分題~!maths 既~~!

x係final exam極mark.

(x+50+60)/3=40
x =120-60-50
x=10

你可以用以下條式check下：
(10/200+60/200+50/200)/3 = 0.2 = 40/200

所以你係final exam度拿10marks out of 200就已經可以keep住average marks係40/200啦.

另外如果要keep住average marks係總成績既40%：

60/200x35%=10.5%

50/200x15%=3.75%

40%-10.5%-3.75%=25.75%

25.75%/50%=0.515

0.515*200=103


你final exam 要拿103 out of 200先可以keep住個average mark係40%.

因爲你條題問得有d唔淸楚所以我兩個都答。你自己斟酌下啦~

let x be the mark,
60x0.35 +50x0.15 +0.5X=40
21+7.5+0.5X=40
0.5X=11.5
X=23