The question is given from ncert Book of class 10th Chapter no. 5 Ex. 5.2 Q. 17. In the following question you have to find the 20th term from the last in the given A.P. Also give the solution with brief details.
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Solution:
The given A.P. is 3, 8, 13, …, 253
d= 5
We can also write the given Arithmetic Progression in reverse order as;
253, 248, 243, …, 13, 8, 5
For the new A.P,
a = 253
d = 248 − 253 = −5
n = 20
i.e using nth term formula, we get,
a20 = a+(20−1)d
a20 = 253+(19)(−5)
a20 = 253−95
a = 158
i.e 20th term from the last term of the Arithmetic Progression is 158.