Your friends presented you with an old fashioned alarm clock. It is 6 p.m. and you have to wake up tomorrow at 7 a.m. You set the clock accordingly. When will it go off?

You have got the hint! The alarm clock is old fashioned, that is why it will not distinguish between 7 a.m. and 7 p.m. So in order to set the clock, you have to do it after 7 p.m!