Samuel has a collection of toy cars. his favorites are the 27 red ones which make up 60%, percent of his collection. how many toy cars does samuel have?

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.

Prove that 16^4-2^13-4^5 is divisible by 11.

Me i’m stuck on all these questions besides the two bottom ones