choose any three digits from 1 to 9 to form a 3 - digit number and each digits is chosen only once. how many of these have the sum of all digit equal to 13

The least 2- digit number that the different of its digits number is .......

The greatest 2-digit number that product of all its digits is 6 is:?

the sum of the digits of a two-digit number is 11. when you reverse its digits you decrease the number by 9 . Find the number

If B is not divisible by 24 and B is the greatest 5 - digit number that the sum of the sum of all digits is 21 then B = ?

a) find the next two term in the sequence: 1; 4; 9; 16; 25;....;.....;
Answer: 
b) find the smallest two-digit number whose number is 7 times the sum of its digits? 
Answer:

choose any three digit from 1 to 9 to from a 3 - digit number and each digit is chosen only once how many of these have the sum of all digit equal to 13

choose any three digit from 1 to 9 to from a 3 - digit number and each digit is chosen only once how many of these have the sum of all digit equal to 13

The sum of the digits of a ten-digit number is epual to 9.What is the product of the digits of this number?