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a)
0.05a+0.04b=9.2---(1)
a-b=40---(2)
由(2)
a=40+b----(3)
(3)代入(1)
0.05(40+b)+0.04b=9.2
2+0.05b+0.04b=9.2
0.09b=7.2
0.9b=72
9b=720
b=80
把b=80代入(3)
a=40+40=80
解(a, b)=(40, 80)
b)
0.2m-0.25n=5----(1)
0.05m+n=14----(2)
由(2)
n=14-0.05m
20n=280-m
m=280-20n---(3)
(3)代入(1)
0.2(280-20n)-0.25n=5
56-4n-0.25n=5
51=4.25n
n=12
m=280-20x12=40

(A)
0.05a+0.04b=9.2 (F1)
a-b = 40
a=b+40 (F2)

Sub F2 into F1:

0.05(b+40)+0.04b=9.2
0.05b+2+0.04b=9.2
0.09b+2=9.2
0.09b=9.2-2
b=80 (F3)

Sub F3 into F2:

a=b+40
a=80+40
a=120

(B)
0.2m-0.25n=5 (F1)
0.05m+n=14
n=14-0.05m (F2)

Sub F2 into F1:

0.2m-0.25(14-0.05m)=5
0.2m-3.5+0.0125m=5
0.2125m-3.5=5
0.2125m=5+3.5
0.2125m=8.5
m=40 (F3)

Sub F3 into F2:

n= 14-0.05m
n=14-0.05(40)
n=14-2
n=12

(A) 0.05a+0.04b=9.2 -------(*)
a-b=40

(*) x 20 => a + 0.8b = 184 ---------(**)
a - b = 40 ---------(***)

(**) - (***) ==> 1.8b = 144
b = 80
From (***), a = 40+b
a = 120

(B) 0.2m-0.25n=5 -------(*)
0.05m+n=14 -------(**)

(*) x 4 => 0.8m - n = 20 -------(***)
0.05m + n= 14 -------(**)

(***) + (**) ==> 0.85m = 34
m = 40
from (**), n = 14 - 0.05m
n = 12