ok,let me explain.The particles in mandarin chinese can be divided into three types:structural particle（的、地、得）,tense auxiliary particle（了、着、过） and modal paricle(or final particle：吗、吧、呢、啊). Obviously,.the question which you referred to above belongs to the 3rd kind:final particle.modal particle:吗/呢(interrogative)、吧(imperative)、啊(exclamative)There is no such an apparent form like Chinese modal particles in English, the English-speaking students often avoid using modal particles to express the appropriate mood. They would like to use intonation rather than modal particles. It results in that the Chinese they said sounded tough and not gentle or native. As for chinese,the most important way to express mood/attitude is using modal particles.

This kind of particle includs 的de、了le、吗ma、呢ne、吧ba、啊a。 The particles 的de and了le are indicative: for instance: ni shi dui de. you are right. wo chi le. I have eaten. The particles 吗ma、呢ne、吧ba are for questions. ta lai ma? will he come here? ta lai ba? it also means will he come here? 吧ba、啊a are imperative and exclamatory for example: zuo ba. please have a seat. duo mei a! How beautiful!

ba is kind of word used after a complete sentence to show your politeness, like "ni mang ba" means please take your time, implies I will not take your time any more or interfere you. ususlly used when one find the guy he talk to has some other to do, so he think he should be leaving. while the ba in "hai xing ba" is pure to make your words sounds a little bit more polite(believe me, it do not matter in this case). while as cherry suggested, ma which also used after a sentence means a question. its function is like to change the order of the verb in a english sentence to requst a yes or no answer. e.g. "ni hao"(you are great.)->"ni hao ma"(Are you ok? or How are you)sometime it can be shorted as "ni hao". It will be really confusing if you try to learn chinese by gramma. better learn it by the 'Rosetta stone'(a software you can download freely on web).

What I learned is 'ma' is interrogative while 'ba' is mainly imperative!

the meaning of "Ni mang ba" depends on its tone,for instance,if it ends with a question mark,it's merely a question which means"are you busy for the moment?",but if it's said in an indicative mood,it means "just go ahead with your business(don't be brothered for me )",which is mostly used as a polite remark in Chinese.so you must pay attention to the tone besides the particles,hope what I explain is helpful to you!