3 ms·
http://www.wolframalpha.com/input/?i=density+of+air+divided+by+the+density+of+helium http://www.wolframalpha.com/input/?i=density+of+air+divided+...
by regularfry 14y ago
http://www.wolframalpha.com/input/?i=density+of+air+divided+by+the+density+of+helium http://www.wolframalpha.com/input/?i=density+of+air+divided+...