Question

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

Answer 1

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

Answer 2

HOLA

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The given Ap is 3 , 8 , 13 ... 253

|•| To find 20th term from the last we have :

L - ( n - 1)d ==> ( Formula )

In this case , L = 253 , N = 20 , D = 5

L - (n - 1)d

253 - (20n - 1 ) 5

253 - (19n)5

253 - 95 = 158

So , 20th term from last is 158

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HOPE U UNDERSTAND