Using the eight digits, 1 - 8 ,
-- There are 40,320 eight-digit permutations.
-- There is 1 eight-digit combination.
22
It is called a 28-digit number!
At 18 digits, you'd be looking at a quantity of 100 Quadrillion. For instance: 111,222,333,444,555,666 is an 18 digit number. 15 digits would be 100 trillion, and 12 digits is 100 billion.
18
There are 18 numbers with 2 digits that are divisible by 5. First 2 digit number is 10 → 10 ÷ 5 = 2 → first 2 digit number divisible by 25 is 5 × 2 Last 2 digit number is 99 → 99 ÷ 5 = 19 4/5 → last 2 digit number divisible by 5 is 5 × 19 → There are 19 - 2 + 1 = 18 numbers with 2 digit divisible by 5.
121
18 of them.
There are 18C4 = 18!/[18-4)!4!] = 18*17*16*15/(4*3*2*1) = 3060 combinations.
18.
22
There are 49 3-digit numbers - from 108 to 990 inclusive.
It is called a 28-digit number!
A very big number! In Europe an 18 digit number is in the trillions. In the US an 18 digit number is in the quintillions. Lots of room for misunderstanding here, best to use scientific notation!
The first number has 19 possibilities. The second has 18, and the third only 17. 19x18x17=5814 possible lock combinations. (If you could repeat, it would be 19x19x19=6859)
At 18 digits, you'd be looking at a quantity of 100 Quadrillion. For instance: 111,222,333,444,555,666 is an 18 digit number. 15 digits would be 100 trillion, and 12 digits is 100 billion.
63
18