difficult maths questions~!10 marks~!

17. b/3 - (5-b) = 3
b/3 -5 + b = 3
b/3 + b = 8
(b + 3b) / 3 = 8 --- (通分母)
4b = 24
b = 6

18. x/3 - x/2 = 1
(2x - 3x)/6 = 1
-x = 6
x = -6

19. 3/4y = 1-1/2y
3/4y = (2-y)/2
4(2-y) = (3y)(2) --- 交叉相乘
8 - 4y = 6y
10y = 8
y = 4/5

20. 2s/3-1 = s+2/5
10s/15 - 15/15 = 15s/15 + 6/15 --- (通分母)
10s - 15 = 15s + 6
5s = -21
s = -21/5

21. r+6/3 = r/2+7/6
6r/6 + 12/6 = 3r/6 + 7/6 --- (通分母)
6r + 12 = 3r + 7
3r = -5
r = -5/3

22. 1/9(h+9) = 5/6-1/2(h+7)
h/9 + 1 = 5/6 - h/2 - 7/2
2h/18 + 18/18 = 15/18 - 9h/18 - 63/18 --- (通分母)
2h/18 + 9h/18 = 15/18 - 63/18 - 18/18
11h = 15 - 63 - 18
11h = -66
h = -6

17. b/3 - (5-b) = 3
b/3 -5 + b = 3
b/3 + b = 8
(b + 3b) / 3 = 8 --- (通分母)
4b = 24
b = 6

18. x/3 - x/2 = 1
(2x - 3x)/6 = 1
-x = 6
x = -6

19. 3/4y = 1-1/2y
3/4y = (2-y)/2
4(2-y) = (3y)(2) --- 交叉相乘
8 - 4y = 6y
10y = 8
y = 4/5

20. 2s/3-1 = s+2/5
10s/15 - 15/15 = 15s/15 + 6/15 --- (通分母)
10s - 15 = 15s + 6
5s = -21
s = -21/5

21. r+6/3 = r/2+7/6
6r/6 + 12/6 = 3r/6 + 7/6 --- (通分母)
6r + 12 = 3r + 7
3r = -5
r = -5/3

22. 1/9(h+9) = 5/6-1/2(h+7)
h/9 + 1 = 5/6 - h/2 - 7/2
2h/18 + 18/18 = 15/18 - 9h/18 - 63/18 --- (通分母)
2h/18 + 9h/18 = 15/18 - 63/18 - 18/18
11h = 15 - 63 - 18
11h = -66
h = -6

17.b/3-(5-b)=3
b-3(5-b)=9
4b-15=9
4b=24
b=6
18.x/3-x/2=1
2x-3x=6
x=-6
19.3/4y=1-1/2y
3=4y-2
5=4y
5/4=y
20.2s/3-1=s+2/5
10s-15=15s+6
-21=5s
s=-21/5
21.r+6/3=r/2+7/6
6r+12=3r+7
3r=-5
r=5/3
22.1/9(h+9)=5/6-1/2(h+7)
6(h+9)=45-27(h+7)
6h+54=45-27h-189
33h=-198
h=-6

17)
b/3-(5-b)=3
b - 3(5-b) = 9
b - 15 + 3b = 9
4b = 24
b = 6

18)
x/3-x/2=1
2x - 3x = 6
-x = 6
x = -6

19)
3/4y=1-1/2y
0.75y = 1 - 0.5y
1.25y = 1
y = 0.8

20)
2s/3-1=s+2/5
15(2s/3-1) = 15(s+2/5)
10s - 15 = 15s + 6
-5s = 21
s = -21/5

21)
(a)
r+(6/3)=r/2+7/6 ???? OR (r+6)/3= r/2+7/6 ????
r + 2 = r/2+7/6
0.5r = -5/6
r = -5/3

(b) (r+6)/3= r/2+7/6 ????
2(r+6) = 3r + 7
2r + 12 = 3r + 7
-r = -5
r = 5

22)
(1/9)(h+9)=(5/6)-(1/2)(h+7)???
h+9 = 7.5 - 4.5(h+7)
h+9 = 7.5 - 4.5h - 31.5
5.5h = -33
h = -6