answer my question if your smartest person

In a jewellery shop there is a gate and you have to say a passcode to enter in it for employees only

once a theif was beside the gate and a employee came and security guard asked question 6 and employee answers 3
Another employee came and security guard ask question 12 and Another employee answers 6

So the theif dressed like an employee and came infront of guard and security guard questions 10 and theif answers 5 but the theif was caught by police how