1) If the expression (12-x)÷(3x) represents a non-negative integer, what is the largest possible integer value of x?
2) If I give my sister 17 dollars, then we will have the same amount of money. If instead she gives me 23 dollars, then I'll have three times as much money as she will have. How much money does she currently have (in dollars)?
(I got 40 for this one, why is it wrong?)
3) Bocephus has a bag full of nickels and dimes. If there are 3 times as many dimes as nickels, and he has $36.05 in his bag, how many nickels does he have?
+9479 2)
Let the amount of money that I have be a .
Let the amount of money that my sister has be b .
If I give my sister 17 dollars, then we will have the same amount of money.
a - 17 = b + 17
Add 17 to both sides of the equation to solve for a .
a = b + 34
If instead she gives me 23 dollars, then I'll have three times as much money as she will have.
a + 23 = 3(b - 23)
Since a = b + 34 , we can substitute b + 34 in for a .
b + 34 + 23 = 3(b - 23)
Simplify both sides.
b + 57 = 3b - 69
Add 69 to both sides.
b + 126 = 3b
Subtract b from both sides.
126 = 2b
Divide both sides by 2 .
63 = b
The sister currently has 63 dollars. And you currently have 63 + 34 dollars, which is 97 dollars. You can try to imagine actually playing out the scenarios, knowing these amounts of money to start with, to help understand. 
+9479 3)
Let the number of nickels in the bag be n .
Let the number of dimes in the bag be d .
There are 3 times as many dimes as nickels. In other words...
The number of dimes is 3 times the number of nickels.
d = 3n
He has $36.05 in his bag. So he has a total of 3605 cents in his bag.
A nickel is worth 5 cents, and a dime is worth 10 cents. So...
5n + 10d = 3605
Substitute 3n in for d .
5n + 10(3n) = 3605
Multiply 10 and 3 to get 30 .
5n + 30n = 3605
Combine like terms.
35n = 3605
Divide both sides of the equation by 35 .
n = 103
