Find the 20th term from the last of the AP 3,8,13,.....253
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Answer:
The given A.P. is 3,8,13,....,253.
Here, a=3, d=8-3=5, t(n)=253, n=?
t(n)=a+(n-1)×d
253=3+(n-1) 5
253= 3+5n-5
253= 5n-2
253+2=5n
255=5n
n= 51.
Therefore, there are 51 terms in the A.P.
Therefore 20th term from last, is
last term-20
51-20=31.
Therefore, we are asked to find the 31st term.
t(31)=3+(31-1)×5
= 3+30×5
= 3+150
= 153.
Therefore, the 20th term from last is 153.
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