Need finding out the recursive formula? ! really stuck on this problem.

On a string instrument, the length of a string varies inversely as the frequency of its vibrations. an 11-inch string has a frequency of 400 cylces per second. find the frequency of a 10-icnch string.

You and a friend went to the movies.you spent half your money on tickets. then you spent 1/4 of the money on popcorn, $2 on candy, and $3 on a soda. if you have $1 left, hiw much money did u take to the movies?

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'