If the fifth and sixth term of a geometric sequence are 112 and 224, what is the average (arithmetic mean) of the second and third terms of the sequence.

The reason of this geometric sequence is 224/112=2 (you multiply the number before by 2 to get the following number)

Then the second term is 112/2^ (5-2) = 14 and the third term is 14*2=28.

And the average of the second and third terms of this sequence is (14+28) / 2=21.