Solution :- Let present age of one friend be x and that of the other 20 – x.
4 years ago age of first friend = x – 4, and that of the other = 20 – x – 4 = 16 – x.
According to question, (x – 4 )(16 – x ) = 48
Or, 16x – x2 – 64 + 4x =48
Or, x2 + 20x – 112 = 0
Or, x2 – 20x + 112 = 0
Here, a = 1, b = – 20, c = 112
D = b2 – 4ac = (– 20 )2 – 4 ×1 × 112 = – 48 < 0.
Hence, the given situation is not possible.