Question

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

Answer 1

so common difference =d= 8 - 3 = 5
last term = a = 253

n = 20 

so using nth = a - (n - 1)d

⇒ x = 253 - 19 x 5

⇒ x = 158 ANSWER

Answer 2

from given data a=3, d= 8-3=5, l=253
l=a+(n-1)d
253=3+(n-1)5
n-1=253-3/5
n-1=50
n=50+1=51
there are 51 numbers in the series
the 20th term from the last will be 32nd term (note that it will not be the 31st term)
so, a32=3+(32-1)5
            = 3+(31)5
            = 3+155
            = 158
therefore the 20th term from the last is 158