to do what, in order to do what ☊ 
sử dụng gì sử dụng để làm gì 
used to doing sth like: đễ làm gì → →
Wofür brauche ich denn diese Einteilung? ☊ 
Vậy anh cần cái bản hướng dẫn này để làm gì? ☊ (Lektion 46, Nr. 661) Sorry to interrupt, but there's someone to see you. ☊ interrupt ☊
What do you need your own computer for? You can use ours. ☊ need ☊
What did you do that for (= why did you do that)? ☊ what for? ☊
'I need to see a doctor.' 'What for?' ☊ what for? ☊