Question

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

Answer 1

Answer:

20th term from last = 158

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

so, there are 51 terms in given series.

now we know, mth term from last =last term - mth term + 1

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

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

use ,

= 3 + 31 × 5 = 3 + 155 = 158

Answer 2

Answer:

for finding 2oth term from last term of ap

an=l-(n-1)×d

253-(20-1)×5

253-19×5

253-95

158= ans