Let us assume amount of money John originally have in his savings account = $x
Money spent on a radio = $72.
Reamining money = x-72.
Money spent on presents for his friends = Two third of remaining money = 2/3 (x-72).
(Because 1 - 2/3 = 1/1 - 2/3 = 1/3)
Reamining money = 1/3 (x-72).
Five twelfths of his remaining money into a checking account = 5/12 * 1/3 (x-72).
( becasue 1 - 5/12 = 1/1 -5/12 = 7/12)
Reamining money = 7/12 * 1/3*(x - 72).
Final remaining money = 7/12 * 1/3*(x - 72) and that is equal to the money donated to charity.
We can setup an equation now.
7/12 * 1/3*(x - 72) = 140.
7/36 (x-72) = 140.
Multiplying both sides by 36.
36 * 7/36 (x-72) = 140 * 36
7(x-72) = 5040.
Dividing both sides by 7, we get
7(x-72)/7 = 5040/7
x-72 = 720
Adding 72 on both side, we get
x-72+72 = 720+72.
x= 792.
Therefore, john originally have $792 in his savings account.
