[ratio and proportion][section 49]

(1.) 7/8 = x/40 here is the problem

8x = 280 cross multiply
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8 8 divide each side by 8

x = 35 divide and cancel

(2.) 9/2 = 63/x here is the problem

9x = 126 cross multiply
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9 9 divide each side by 9

x = 14 divide and cancel

(3.) 11/x = 132/24 here is the problem

132x = 264 cross multiply
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132 132 divide each side by 132

x = 2 divide and cancel

(4.) x/13 = 10/65 here is the problem

65x = 130 cross multiply
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65 65 divide each side by 65

x = 2 divide and cancel

(5.) 21/5 = x/2.5 here is the problem

5x = 52.5 cross multiply
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5 5 divide each side by 5

x = 10.5 divide and cancel

(6.) 29/7 = x/1.75 here is the problem

7x = 50.75 cross multiply
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7 7 divide each side by 7

x = 7.25 divide and cancel

(7.) 17/2 = 8.5/x here is the problem

17x = 17 cross multiply
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17 17 divide each side by 17

x = 1 divide and cancel

(8.) (b + 3)/5 = 7/10 here is the problem

10b + 30 = 35 cross multiply

-30 -30 subtract 30 from each side
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10b = 5 subtract
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10 10 divide each side by 10

b = 1/2 reduce and cancel

(9.) 3/z = 8/(z + 5) here is the problem

8z = 3z + 15 cross multiply

-3z -3z subtract 3z from each side
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5z = 15 subtract
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5 5 divide each side by 5

z = 3 divide and cancel

(10.) (r + 4)/2 = (r - 3)/1 here is the problem

2r - 6 = r + 4 cross multiply

+ 6 + 6 add 6 to each side
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2r = r + 10 add

-r -r subtract r from each side
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r = 10 subtract