If I give my brother 5 dollars, then we will have the same amount of money. If instead he gives me 25 dollars, then I'll have twice as much money as he will have. How much money does my brother currently have (in dollars)?
Let x be your starting amount and y be your brothers.
Then both the following equations are true.
x-5 = y+5
2(y-25) = x+25
Starting with the 2nd one: 2(y-25) = x+25
2y = x+75
y = 1/2x + 37.5
For the first one: x-5 = y+5
x = y+10
So we can plug that into our old equation.
y = 1/2(y+10) + 37.5
y = 1/2y+5+37.5
y = 1/2y + 42.5
1/2y = 42.5
y = 85
So logically, X should equal 95
The answer is 85.