Brain teaser - hour glass

#1

please explain 2 solution in proper way how to do it ??..i am not understand your concept

#2

hello @vishal_sangal_123
are u asking about that 15min question.
here is the solution->
you first turn on both glasses, so when one glass goes off, time remaining in other glass is 4 minutes(11-7), now when this 4 minutes are over, again turn on the glass with 11 minutes, so now you measured 15 minutes(4+11), total time taken to measure 15 minutes is 22 minutes.(as you waste 7 mins at starting to measure 4 minutes)