What Has Numbers On The Outside And Letters On The Inside? October 27, 2017June 15, 2016 by Bhavini Share the riddle when you get the correct answer. What has numbers on the outside and letters on the inside? Leave your answers in the comment section. Show Answer Answer: A Letter Box or A Mailbox. The letter box or mailbox has the house number outside and letters or mail inside. Were you able to figure out this correct answer? Do share the riddle with all the kids that you know, they will surely enjoy and thank you for it.