Alfred and Charlie have the same amount of money. After Alfred spent 2/7 of his money and Charlie spent $900, Charlie has $300 less than Alfred. How much money does each of them have at first?

Answer 1

A's amount --- x
C's amount --- x

after spending spree:
A had 5/7 x or 5x/7
C had x - 900

A - C = 300
5x/7 - (x-900) = 300
times 7
5x - 7x + 6300 = 2100
-2x = - 4200
x = 2100

each had 2100

Answer 2

1 - 2/7 = 5/7
(5/7) A - 300 = C- 900
but
A = C
(2/7) A = 600
A = C = 300* 7 = 2100
==================
check
==================
(5/7) 2100 = 1500 = what A had left
2100 - 900 = 1200 = what C had left
1500 - 1200 = 300 sure enough