Billy has a collection of baseball cards that he has separated into two different value categories. His common cards
are worth $0.50 each, while his premium cards are worth $1.00 each. Together, Billy's entire baseball card collection
of 124 cards is worth $81.50.
Which of the following systems of equations models Billy's baseball card collection?

What is the expression in factored form? 225x^2 - 144 a. 9(5x+4)^2 b. 9(5x-4)^2 c. 9(4x+5)(4x-5) d. 9(5x+4)(5x-4)

Acertain volume of water contains 100000 hydrogen atoms and 50,000 oxygen atoms how many hydrogen atoms are in a volume of water containing 4 million oxygen atoms

Aclassroom is made up of 11 boys and 14 girls. the teacher has four main classroom responsibilities that she wants to hand out to four different students (one for each of the four students). if the teacher chooses 4 of the students at random, then what is the probability that the four students chosen to complete the responsibilities will be all boys?