You have two ropes and a box of matches. Each rope takes exactly one hour to burn, but they may not necessarily burn evenly – i.e., the first half might burn in the first 10 minutes and the second in the remaining 50). What durations of time can you measure using the 2 ropes? Times do not have to start when the first rope is lit.
Note that this is a multiple choice question. Mark all the times which are measurable.