5[0.5(m-0.4)-0.1m]=2-0.5(m=4)

m=4﹖
圖片參考：http://hk.yimg.com/i/icon/16/17.gif

如果算式是m+4，
5[0.5(m-0.4)-0.1m]=2-0.5(m+4)
5[0.5m-0.2-0.1m]=2-0.5m-2
2m-1=0-0.5m
2.5m=1
m=2/5
如果算式是m-4，
5[0.5(m-0.4)-0.1m]=2-0.5(m-4)
5[0.5m-0.2-0.1m]=2-0.5m+2
2m-1=4-0.5m
2.5m=5
m=2

左邊個(m=4)，你係咪想話(m+4) ar。

計呢d數，只要慢慢折，唔好心急，就唔會亂ga la。

5[0.5(m-0.4)-0.1m] = 2-0.5(m+4)
5(0.5m-0.2-0.1m) = 2-0.5m-2
5(0.4m-0.2) = -0.5m
0.2m-2.5 = -0.5m
0.2m+0.5m = 2.5
0.7m = 2.5
m = 2.5/0.7=3.5714 (corr to 4 d.p.)