John drives 50 km/h for one hour and 100 km/h for one hour. instantaneous speed each hour:
average speed for the two hours:

How is it possible for someone to put an ear to a wall and hear someone in the next room?     a.sound waves can travel though solids.    b.the waves travel from room to room via air.    c.there must be some air in the wall so the sound can travel through it.    d.sound waves change to electromagnetic waves and then back again.