Question

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

Answer 1

an=55
a =1
d=3
an=a+(n-1)d
55=1+(n-1)3
55=1+3n-3
57=3n
n=19.
hope it help u.

Answer 2

$55 = 1 + (n - 1)3$
$55 = 1 + 3n - 3$
$55 = 3n - 2$
$57 = 3n$
$n = 57 \div 3$
$n = 19$