Answer:

(i) 

Given,

A.P is 3, 8, 13,…

a₁ = a = 3

a₂ = 8

Common difference, d = a₂ – a₁ = 8 – 3 = 5

a_n = a + (n – 1)d

a_n = 3 + (n – 1)5

= 3 + 5n – 5

= 5n – 2

(Put, a_n = 248)

∴ 5n – 2 = 248

= 248 + 2

= 250

= 250/5

= 50

50^th term of given A.P is 248.

(ii) 

Given,

A.P is 84, 80, 76,…

a₁ = a = 84

a₂ = 88

Common difference, d = a₂ – a₁ = 80 – 84 = -4

a_n = a + (n – 1)d

a_n = 84 + (n – 1)-4

= 84 – 4n + 4

= 88 – 4n

Put,

a_n = 0

88 – 4n = 0

-4n = -88

n = 88/4

= 22

22^nd term of given A.P is 0.