OK here is a problem that was in my exam today. Just wanna check if I've done it correct.

An inverted cone with a height of 50 cm was originally filled with oil. Then some of the oil was removed and now the remaining oil has a height of 20 cm. find the percantage of the oil that was removed.

this is how i did it-

length ratio- 20:50 = 2:5 (oil:cone)

volume ratio- 8:125. (oil:cone)

oil removed- 125-8 =117

% oil removed- 11700/125 = 93.6%

is this method correct????

NOTE

some students did- 3:5 (removed:cone) and calculated the percentage.