Insert 4 A.M.s between 4 and 19.
Let A1, A2, A3, A4 be the 4 AM Between 4 And 19
Then, 4, A1, A2, A3, A4, 19 are in AP
We know,
An = a + (n - 1)d
a6 = 19 = 4 + (6 - 1)d
d = 3
Hence,
A1 = a + d = 4 + 3 = 7
A2 = A1 + d = 7 + 3 = 10
A3 = A2 + d = 10 + 3 = 13
A4 = A3 + d = 13 + 3 = 16