Question 803738
For solving this problem, Bill will be {{{y}}} and Jim will be {{{x}}}.

To start off, we know that Bill has double the amount that Jim has.  
You can think of this as 2 Jims equal 1 Bill.  
You would write this as {{{y=2x}}}.

Now if Jim were to be given $2.50 he would have 3 times as much as Bill.  
This equation can be written as {{{2.50+x=3y}}}.  
Jim plus the $2.50 is equal to 3 times Bill.

We are going to solve for Jim first.  
We want to solve for {{{x}}} since Jim is {{{x}}}.  
That means u will plug {{{y=2x}}} into {{{2.50+x=3y}}}.  
Since {{{y=2x}}}, you can replace the {{{y}}} in {{{2.50+x=3y}}} with {{{2x}}}. 
Solve for {{{x}}}.

{{{2.50+x=3(2x)}}}        Multiply 3*2x
{{{2.50+x=6x }}}           Subtract {{{x}}} from both sides
{{{2.50=5x }}}                Divide both sides by 5
{{{x=.50}}}

We know now Jim originally had $.50.

Now let's figure out what Bill originally had.
We need to solve for {{{y}}}.
{{{2.50+x=3y}}} can also be written {{{x=3y-2.50}}}.
Now plug {{{x=3y-2.50}}} into {{{y=2x}}}.
You can replace the {{{x}}} in {{{y=2x}}} with {{{3y-2.50}}}.
Now solve.

{{{y=2(3y-2.50)}}}      Multiply it out.
{{{y=(2*3y)-(2*2.50)}}}
{{{y=6y-5}}}               Subract 6y from both sides.
{{{-5y=-5 }}}              Divide each side by -5.
{{{y=1}}}

We have now figured out that Bill started with $1.00.

The answer for this problem is Jim originally had $.50 and Bill originally has $1.00.