Home / study / math / algebra / questions and answers / fill in the blank with the question: fill in the blank with the appropriate problem fill in the blank with the appropriate problem number 18 19 or 20 and then give the solution you may use scientific notation rounded to the nearest tenth if necessary. 18. 26·26·26·26 counting principles. 19. 900c10 combination 20. 90! ÷(90-10)! ·10! combination. 24. problem 21 can be solved with the setup given in problem the solution to the problem is: (problem 21) in a crowd of 90 people how many ways can 10 digital music players be given away. 25. problem 22 can be solved with the set of giving him problems a solution to problem is. (problem 22) a computer randomly generates a four-letter passwords how many passwords are possible if letters may repeat. 26. problem 23 can be sold with the setup given in problem solution to problem 23.