B1. Brenda wants to fill bags with an inexhaustible supply of red and blue marbles. In each bag, she puts more red marbles than blue marbles, and in each bag, there are no more than 25 marbles. For example, she can make a bag with 6 red and 2 blue marbles or a bag with 1 red marble and 0 blue marbles. How many differently filled bags can she make in total?
B1. 169

Brenda can make 25 different bags without blue marbles, as she can put 1 to 25 red marbles in a bag. There are 23 different bags possible with 1 blue marble, as 2 to 24 red marbles can be added. With 2 blue marbles, there are 21 possibilities, namely with 3 to 23 red marbles. In total, there are $25+23+\ldots+1=169$ different bags that Brenda can make.