0 votes 0 votes How many strings of four decimal digits do not contain the same digit twice? end with an even digit? have exactly three digits that are $9s?$ Combinatory kenneth-rosen discrete-mathematics counting descriptive + – admin asked Apr 28, 2020 • edited Apr 28, 2020 by Lakshman Bhaiya admin 702 views answer comment Share Follow See all 0 reply Please log in or register to add a comment.