How do we decide if 中 is ちゅう or じゅう ?
For example, in this sentence １０人中３人はビデオを持っている which pronunciation should we use?
What about this: そのピアニストの演奏中、彼らは一心に耳を傾けた。
Note that in some cases, both can be used and the only way to tell would be from context (e.g. an expression followed by に is more likely to be ちゅう) or in speech:
"out of" is 「ちゅう」, "through" is 「じゅう」.
That second example is "during", so 「ちゅう」.