[ratio and proportion][section 49]

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

8x = 280         cross multiply
____ ____
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
___  ____
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
_____  ___
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
____  ____
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
___ _____
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
___ _______
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
____ ___
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
__________________
10b    =  5         subtract
____     _____
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
__________________
5z =      15            subtract
___      _____
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
____________________
2r      = r + 10  add

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