Answer:
A1, A2, A3, A4 – 4 AM Between 4 and 19
4, A1, A2, A3, A4, 19 are in AP.
By using the formula,
d = (b-a) / (n+1)
d = (19 – 4) / (4 + 1)
d = 15/5
d = 3
A1 = a + d = 4 + 3 = 7
A2 = A1 + d = 7 + 3 = 10
A3 = A2 + d = 10 + 3 = 13
A4 = A3 + d = 13 + 3 = 16