A. Use the factorial function in your answer: 11 + 3! (1*2*3, which equals 6) + 13 = 30
B. Change the mathematical base system of the equation in certain places (this can give an answer with multiple bases or a single base): For single bases: For multiple bases... 9_10+9_10+9_10=30_9. A number which appears as "30" when written in a different base system doesn't represent "thirty" in base ten. When written in base 9 as 30_9, is equivalent to twenty-seven in base ten: (27_10). Or using all the same base: 13_5+11_5+1_5=30_5 in base five, which is equivalent to (8_10+6_10+1_10=15_10) in base ten. Or 13_9+15_9+1_9=30_9 in base nine.
C. Use the commas given in the question to your advantage: In many countries, the comma (,) is used instead of the full stop (.) to represent a decimal point. For example "3.5" (three and a half) can be written as "3,5". This allows for the solution 11,3 + 15,7 + 3 = 30. Only use numbers in two of the brackets: You could leave one of the brackets blank and have the answer as () + (15) + (15) = 30. The first fifteen represents a fifteen with a "unary plus" (+15) and the second fifteen added to the first one gives us thirty. The first bracket is left empty.
Rotate one of the accepted numbers so that it resembles a different number: If the number 9 is rotated 180 degrees then it can resemble the number 6. 6 (an upside-down number "9") + 9 + 15 = 30.