Question

find the 20th term for last term of AP 3,8,13....253​

Answer 1

Answer:

a = 3, d = 5

Now, 253 = a + (n + 1) d

⇒ 253 = 3 + (n -1) x 5

⇒ 253 = 3 + 5n – 5 = – 2

⇒ 5n = 253 + 2 = 255

⇒ n = 255/5 = 51

Therefore, 20th term from the last term = 51 – 19 = 32

a32 = a + 31d

= 3 + 31 x 5

= 3 + 155 = 158

Thus, required term is 158

HOPE IT HELPS YOU

Answer 2

AP =3,8,13....253​

a = 3

d= 5

now reversing the AP

ie.

AP= 253........13,8,3

a= 253

d= -5

a20= ?

a20=a+19d

a20= 253+19(-5)

a20=253- 95

a20=158

hope it helps ..

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