Question

Assume that you select digits from the set {2,3,5,6,7,8} to form a number between 20 and 800.

(1) How many such numbers can be formed if digits are not repeated?
(2) How many such numbers can be formed if digits can be repeated?

Answer 1

all 2 digit numbers are above 20 so u are good there
then all 3 digit numbers that dont start with 8 are below 800

Answer 2

no repeition
2 digit numbers
6*5

3 digit numbers with out 8 in beginning
5*5*4

Answer 3

with repetition alloved
2 digit numbers
6*6
3 digit numbers
5*6*6