Insert 4 A.M.s between 4 and 19.
Let A1,A2,A3,A4 be the 4 A.M.s between 4 and 19.
Then,
4,A1,A2,A3,A4,19 are in A.P. of 6 terms.
An=a+(n−1)da6=19=4+(6−1)d
Or d = 3 ...... (i)
Now,
A1=a+d=4+3=7A2=A1+d=7+3=10A3=A2+d=10+3=13A4=A3+d=13+3=16
The 4 A.M.s between 4 and 19 are 7, 10, 13, 16.