How many integers between 10 and 100 can be formed by
the digits 1,2,3,4,5 if no repetition is allowed?
Choose the first digit any of the 5 ways.
Choose the second digit any of the remaining 4 ways.
Answer: 5*4 = 20
12, 13, 14, 15, 21,
23, 24, 25, 31, 32,
34, 35, 41, 42, 43,
45, 51, 52, 53, 54.
How many can be formed if repetition is allowed?
Choose the first digit any of the 5 ways.
Choose the second digit any of the 5 ways.
Answer: 5*5 = 25
11, 12, 13, 14, 15,
21, 22, 23, 24, 25,
31, 32, 33, 34, 35,
41, 42, 43, 44, 45,
51, 52, 53, 54, 55.
Edwin
