The importance of 'same' in Fraction questions

When it comes to fraction questions, pay attention to the 'same' word if it appears in the question. It will be the key to solve the question. Here is an example.

Question:

Adam and Bella had $5100 altogether. After Adam spent 4/5 of his money and Bella spent 5/7 of her money, they had the same amount of money left. How much money did each of them have at first?
 
Solution:

Key info: 'same amount of money left' 

Adam left 1 unit and Bella left 2 units. It means Adam's 1 unit is equal to Bella's 2 units. 

Change Adam's units to Bella's Units as shown in the table below:

17 units -> $5100
1 unit -> $300
Adam 10 units -> $3000
Bella 7 units -> $2100