suppose i attempted only 2-4 questions of mathematics portion in b.arch and managed to get 170+ in aptitude portion and 70+ in drawing. Would i be able secure admission in good colleges?
It depends on the overall rank. However if you do so, you can get a good rank but again it depends (on the difficulty of the three subjects separately). If the aptitude part is tough enough and mathematics is not and then of you score 170+ in aptitude and only 3-4 questions in mathematics then you will get a much better rank.
Based upon your overall rank, admission will be made to the different institutes.
In general, you will get a decent college by doing so (if your luck is not that much bad).