A prawn seller bought 250 kg of prawns at $3.50 per kg. He sorted them out into 3 grades, A B and C which were sold at $10.00 per kg, $8.00 per kg and $6.00 per kg respectively. How much profit would he make if 0.2 of the prawns were of Grade A, 0.25 of the remainder were Grade B and the rest were of Grade C?
The total cost of buying the prawns was 250 * $3.50 = $<<250*3.5=875>>875.
Of the prawns, 0.2 * 250 = <<0.2*250=50>>50 kg were of Grade A.
So, there were 250 - 50 = <<250-50=200>>200 kg left.
0.25 * 200 = <<0.25*200=50>>50 kg were of Grade B.
So, the remaining 200 - 50 = <<200-50=150>>150 kg were of Grade C.
Hence, the seller earned 50 * $10 = $<<50*10=500>>500 for selling the Grade A prawns.
He also earned 50 * $8 = $<<50*8=400>>400 for selling the Grade B prawns.
And he earned 150 * $6 = $<<150*6=900>>900 for selling the Grade C prawns.
Therefore, the total earning of the seller was $500 + $400 + $900 = $<<500+400+900=1800>>1800.
Thus, the profit he made is $1800 - $875 = $<<1800-875=925>>925. Answer: \boxed{925}.