Hey Nadeshiko.
Hint: Calculate the arithmetic mean as a function of n (n is the first number) and derive an inequality based on this. (you are going to have (10n + blah)/10 = 3 for your mean relationship).
If "x" is the first of "10 consecutive even numbers" then the numbers are x, x+2, x+ 4, x+ 6, x+ 8, x+ 10, x+ 12, x+ 14, x+ 16, and x+ 18
What is the mean of those 10 numbers?
For the second, note that these numbers are of the form 133, 233, 433, 3x3 or 33x where x can be any digit from 0 to 9 except 3.