there must be many people dancing 变反意疑问句?

There must be many people dancing, aren't there?
当must用来表示对现在的情况进行“推测”时,反意疑问部分要根据must后面的动词采用相应的形式.
例 He must be good at maths, isn’t he? 他数学一定学得很好,是吗?