Sabrina bought cookies and brownies for her party. She bought a total of 20 items. The cookies cost $1.50 each and the brownies cost $1 each. The total amount that she spent was $22.50. Write two equations to represent the situation. Use x for cookies and y for brownies. Solve the equations and determine how many cookies and brownies she bought. Write the answer as an ordered pair. (x, y)

30 people weigh 160 pounds or more

there is only one way to arrange all the eight relative to each other because they are not distinct. we have

now there are nine places to place an (and not more than one in one place).   because we have four symbols, we need to choose four of these nine places to insert an . order does not matter because the are not distinct.

thus there are 1 · c(9,4) ways, or, if we calculate it,

thus there are 126 ways to form such "words."