Behind my house is a big field. every winter after a few rainstorms the field seems to attract lots of puddles,mud,and frogs. the frogs are quiet for the most part.however when one starts croaking,they all do,which serves to attract more frogs.and then all seem to shut up at once. one night 30 frogs were present and they all started croaking at 11:p.m. they all crock for a number of seconds equal to the number of frogs present. after that amount of time, 1 frog drops out at the beginning of every subsequent second. they all stop abruptly after the second in which they realize that only half of them are croaking. two more frogs arrive every 20 minutes, and this starts the whole process over again with massive croaking. (every 20 minutes means that new frogs arrive at 11:20,11:40,12:00 and so on.)how many seconds of croaking took place from when i went to bed at 11:p.m.( and they started croaking.) until i got up at 7:10 a.m.?
