Question

Find 20th term from end of the A.P. 3, 7, 11, .... 407.

Answer 1

l = last term = 407
d= common difference = 7-3 = 4
therefore, 20th term from the end = 407 + (20-1)(-4). [ because nth term from the end = l+(n-1)(-d) ]
= 407+19(-4)
= 407-76
= 331

Answer 2

Answer:

331

Step-by-step explanation:

Sol: Here a = 3, d = 4, tn = 407

∴ tn = a + (n – 1)d 

∴407 = 3 + (n – 1)c

∴ n = 102

⇒ 20 th term from last = (102 – 20 + 1) term = 83rd term

∴ t83 = 3 + (83 – 1)4 = 331