Question

insert two arithmetic means between each pair. the pair is -27 and 33

Answer 1

Let the two numbers be a and b
your series:
-27, a, b, 33

T4 - T1 = 33 - (-27) = 60
60/3 = 20
so d (common difference) = 20
so a = -27 + d
and b = a + d

a = -7
b = 13

Your new series:
-27, -7, 13, 33