Question

Which terms of the a.p 1,4,7,...is 55?

Answer 1

a = 1

d = T2 - T1 = 4 - 1 = 3

L = 55

=> a + (n-1) d = 55

=> 1 + (n-1)(3) = 55

=> (n-1) (3) = 54

=> n - 1 = 18

=> n = 19


19th term of the given AP is 55

Answer 2

a. p
$term{n}= 55$
a
$a + ({n - 1} )\times d = 55$
$1 +( n - 1) \times 3 = 55$
$1 + 3n - 3 = 55$
$3n = 55 + 2$
n
$n = 19$