Mina spent 4 hours visiting her friend. they spent 2/3 of their time together riding bikes. how many hours did mina and her friend spend riding bikes? (sorry if it doesn't make sense)

2 hours and 30 minutes because if you divide the four hours by three you get 1 hour and 20 minutes you add 1 hour and 20 minutes by itself and you get your answer :)

Diagonals of regular pentagon trisect all the interior anglesSo, angle ABO will be 1/3 times interior angle ABCso, angle ABO = 36 similarly angle BAO = 36
so angle AOB will be 180 -36-36(because angle in a triangle sum upto 180)
and since EOC is vertical to AOBEOC = AOB