"In a market, four brokers A, B, C and D, account for 20%, 15%, 20.5% and the rest for D, of the total volume of contracts traded, respectively. Of the volume of each broker, 20%, 5%, 2% and 70%, respectively, are future contracts in dollars. A contract is chosen at random and this is a future successful contract in dollars. What is the probability of it having been traded by broker A?"

The answer I got is 0.1284, but that is not an option in the multiple-choice assignment.