Question

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

Answer 1

Answer:

Given series is 3, 8, 13, ...... 253

here, first term , a = 3

common difference , d = 5

Let us find total number of terms at first.

use \bf{T_n=a+(n-1)d}

=> 253 = 3 + (n - 1)5

=> 250 = 5(n - 1)

=> n - 1 = 50

=> n = 51

so, there are 51 terms in given series.

now we know, mth term from last =last term - mth term

so, 20th term from last = 51 - 20 + 1 = 32

hence, 20th from last = 32th term from first

use , \bf{T_{32}=a+(32-1)d}

= 3 + 31 × 5 = 3 + 155 = 158

hence , 20th term from last = 158

Answer 2

Step-by-step explanation:

Given series is 3, 8, 13, ...... 253

here, first term , a = 3

common difference , d = 5

Let us find total number of terms at first.

use

=> 253 = 3 + (n - 1)5

=> 250 = 5(n - 1)

=> n - 1 = 50

=> n = 51

= 3 + 31 × 5 = 3 + 155 = 158