Question

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

Answer 1

Answer:

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Answer 2

Answer:

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Step-by-step explanation:

Solution :

We have, l = Last term = 253

and,

              d = Common difference = 8 - 3 = 5

∴ 20th term from the end = l - (20 - 1)d

                                          = l - 19d

                                          = 253 - 19 × 5

                                          = 253 - 95 = 158

OR IN DETAIL:-

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

→hence, 20th term from last = 158