Because we are given a ratio, whatever Jacob's allowance is should be 20.5/4.1 times Melanaie's allowance. So the easiest way to do this problem is to set up a system of equations to find out how much money Melanaie gets.
Because we know the Melanaie to Jacob ratio is 4.1 to 20.5, we know that the money Melanaie gets (m) will be multiplied by 4.1 and the money Jacob gets (j) will be multiplied by 20.5 so that they will equal each other. So our equation will look something like this: 4.1*m=20.5*j. The easiest way to solve this would just be to plug in 5 for the money Jacob gets, then solve for m. Because 20.5*5 is 102.5, our equation can now look like this: 4.1*m =102.5. Next, to get m alone, we have to divide both sides by 4.1, making our equation look like this: m =102.5/4.1. Now all we have to do is divide 102.5 by 4.1 to get 25 for m! This means when Jacob gets $5 for his allowance, Melanaie will get $25!
