Question

Find the ${17}^{th}$ term from the end of the AP: 1,6,11,16…..211,216

Answer 1

Here
first term = 1
common difference = 6-1 = 5
now,
use formula,
tn=a+(n-1)d
216=1+(n-1)5
215-5 = n-1
n=44
hence 44 terms in this series
so, from last 17th term = from first (44-17+1)th term = 28th term from first.
Now,
28th term = a(28-1)d
= $1+27\times 5=136$.