IS question 15點15點15點15點

http://www.smokefree.hk/tc/content/web.do?page=SecondhandSmoking

吸煙者吸啜捲煙時吸入肺部後再呼出的煙氣，稱為「主流煙」，主流煙只 佔所有捲煙煙霧的15% ; 而煙草燃燒時直接釋放出的煙氣，約佔85%，稱 為「支流煙」。

From the info above, I think it is safe to answer ''15%''.

2012-01-11 02:37:16 補充：
提醒你！請記得處理問題！如需刪題，請先說明之！謝！

Only__10__% of the cigarette smoke is breathed in by the smoker.The rest is released into the air.

Only a few % of the cigarette smoke is breathed in by the smoker . The rest is released into air . Actually when the smoker lights a cigarette , the burning of the tobacco releasing all the harmful chemicals out & sucked into the lung . Some of them are retained by the filter however most is expelled out by the smoker .