A two-digit number has 3 as its tens digit, and when a digit is inserted in the middle to form a three-digit number, this three-digit number is exactly 9 times the original two-digit number. The new three-digit number is $\qquad$
【Analysis and Solution】
Number problem.
The unit digit has not changed, and the only unit digits that remain the same when a number is $\times 9$ are 0 and 5; and $30 \times 9=270$ (the hundreds digit is not 3, so it is discarded), $35 \times 9=315$;

That is, the new three-digit number is 315.