140
a 8-digits palindromic number is a number consisting of a 4-digits number written and then written backward, i.e. 1234 4321 so there are as many palindromic 8-digits numbers as 4-digits numbers so from 1000 to 9999, so there are 8999 palindromic 8 digits number (I assumed that 00011000 is not to be considered as a valid 8 digit number)
Single digit numbers is not correct. Squares of numbers will appear odd number of times in a multiplication table: 1², 2², 3², 4², 5², 7², etc....
The answer will depend on how many digits there are in each of the 30 numbers. If the 30 numbers are all 6-digit numbers then the answer is NONE! If the 30 numbers are the first 30 counting numbers then there are 126 combinations of five 1-digit numbers, 1764 combinations of three 1-digit numbers and one 2-digit number, and 1710 combinations of one 1-digit number and two 2-digit numbers. That makes a total of 3600 5-digit combinations.
3456 is divisible by the single digit numbers 1,2,3,4,6,8,9
-12
3 digit numbers are lessthan 4 digit numbers
By including the number 1000, the digit 1.
1 digit number: only 1 number 2 digits number: 18 numbers 3 digits number: 76 So there are 95 numbers containing 9.
There is one significant digit in the number 10, as written.
There are 17 such numbers.
9
98
A 3 or 4 digit number.
There is a possible confusion over how the last part of your question ("contain no 5") can be interpreted:it could be a badly written shorthand of the word number: "Nº" also written "No." also written "No" and very badly written as "no", meaning "contains the number 5", meaning "the number 5" - the number between 4 and 6 and less than 10;it could be a badly written shorthand of the word number: "Nº" also written "No." also written "No" and very badly written as "no", meaning "contains the number 5", meaning "the digit 5" - the digit 5 in any place value column;It negates the sense so that "contain no 5" means "do not contain the digit 5".In interpretation number 1 there are no such numbers, as 5 is less than 10 and all two digit numbers are greater than, or equal to 10 (I suspect that this meaning is definitely not intended).There are 90 two digit numbers (10 - 99); of them:9 contain a 5 as the second digit: 15, 25, ..., 9510 contain a 5 as the first digit: 50, 51, ..., 59So there are 19 of the digit 5 used.However, 55 is counted twice, meaning there are 18 numbers which contain the digit 5. (This is the solution to the interpretation number 2.)Which means there are 90 - 18 = 72 numbers which do not contain the digit 5. (The solution to interpretation number 3, which I suspect is the required answer.)Use whichever solution meets your intended interpretation of the question you wrote.
3897
The ratio of the number of one-digit prime numbers to the number of one-digit composite numbers is one to one. The one-digit prime numbers are 2, 3, 5, and 7. The one-digit composite numbers are 4, 6, 8, and 9. Therefor, the ratio is 4:4, which simplifies to 1:1.
There are four of each.