According to Nielson Media Research, 75% of all US households have cable television. Erica conducts a random sample of 1000 households in DuPage County and finds that 800 of them have cable. What might Erica conclude?

I am not sure if there is work that I should be including... it seems like the sample size is not representative of the whole US... maybe 1 county is not a good representation of the whole country. I am really not sure what I am supposed to be doing with this problem. Thanks for any help!