4
73 is the largest two-digit number that is prime and has prime numbers for both of its digits.
Mental math like if 12 into 72 it will not be a double digit if you divide 100 by 10 it will be double digits. Most times if you have a tripple digit number and divide it by double digit the answer will be a double digit.
In the numbers 1-9 each number has 1 digit and there are 9 of them, so that's 9.In 10-99 each number has 2 digits, and there are 90 of them: 2x90 = 180There are 900 three digit numbers [100 through 999]: 2700 digits.There are 9000 four digit numbers: 36000 digits.90,000 numbers with five digits: 450,000 digits.900,000 numbers with six digits: 5,400,000 digits.Then 1 number with seven digits: 7 digits.Add them up and you have 5,888,896 digits.
Any number that has 4 or 5 digits. A digit in a number is one number place. 1 has 1 digit, 11 has 2 digits, 111 has 3 digits, and so on.
73 is the largest 2 digit number that is both prime and has prime numbers for both of its digits.
2
There are 9 digits that can be the first digit (1-9); for each of these there is 1 digit that can be the second digit (6); for each of these there are 10 digits that can be the third digit (0-9); for each of these there are 10 digits that can be the fourth digit (0-9). → number of numbers is 9 × 1 × 10 × 10 = 900 such numbers.
Digits is how many numbers you have in a number. If you have the number 4 it has one digit if you have the number 20 it has two digits and if you have the number 558 it has three digits. So basically in the number 1085 it has 4 digits because there is 4 numbers in it, the numbers are 1,0,8 and 5. Hoped you understand.
12689 14689 12489
There are only two smaller 3-digit numbers and both of them have repeated digits.
It is possible to create a 3-digit number, without repeated digits so the probability is 1.