Let $A_1, A_2, A_3, A_4, A_5$ be numbers between 8 and 26 such that 8, $A_1$, $A_2, A_3, A_4, A_5$, 26 are in A.P., Here a = 8, l = 26, n = 7 ∴ 26 = 8 + (7 – 1) d ⇒ 6d = 18 ⇒ d = 3 Thus $A_1$ = a + d = 8 + 3 = 11; $A_2$ = a + 2d = 8 + 6 = 14 $A_3$ = a + 3d = 8 + 9 = 17; $A_4$ = a + 4d = 8 + 12 = 20 $A_5$ = a + 5d = 8 + 15 = 23 Hence five numbers between 8 and 26 are 11, 14, 17, 20, 23.