Find the 20th term from the last term of the A.P. 3, 8, 13, …, 253. Q.17

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The best solution for the class 10th of the important question of arithmetic progressions of ncert of class 10th. How i solve in easy way Find the 20th term from the last term of the A.P. 3, 8, 13, …, 253

Given A.P. is3, 8, 13, …, 253

Common difference, d= 5.

Therefore, we can write the given AP in reverse order as;

253, 248, 243, …, 13, 8, 5

Now for the new AP,

first term, a = 253

and common difference, d = 248 − 253 = −5

n = 20

Therefore, using nth term formula, we get,

a_{20}=a+(20−1)da_{20}= 253+(19)(−5)a_{20}= 253−95a= 158Therefore, 20

^{th}term from the last term of the AP 3, 8, 13, …, 253.is 158.