Miller park sits on one square city block 300ft on each side. the city wants to get an estimate of how much it would cost to put a sidewalk across the park, diagonally, joining a pair of opposite corners. the city figures it will cost $25 per linear foot to have a company carve out and pour the concrete for the sidewalk. how much will the project cost?

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."