Let the 4 numbers be a, a + d, a + 2d, a + 3d.

Sum of 4 numbers in A.P = 50

a + a + d + a + 2d + a + 3d = 50

⇒ 4a + 6d = 50

⇒ 2a + 3d = 25 --------------(1)

Given the greatest number is 4 times the least.

4(a) = a + 3d

4a – a = 3d

a = d

Putting, a = d in (1), we obtain

5d = 25

d = 5

⇒a = 5

∴ First four terms are 5, 10, 15, 20.