Element X decays radioactively with a half life of 12 minutes. If there are 510 grams of Element X, how long, to the nearest tenth of a minute, would it take the element to decay to 11 grams?

sorry but i cant draw that

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."