NCERT Solution Class X Mathematics Arithmetic Progressions Question 17 (Ex 5.2)

Question 17:

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

Answer:

Given A.P. is

3, 8, 13, …, 253

Common difference for this A.P. is 5.

Therefore, this A.P. can be written in reverse order as

253, 248, 243, …, 13, 8, 5

For this A.P.,

a = 253

d = 248 − 253 = −5

n = 20

a20 = a + (20 − 1) d

a20 = 253 + (19) (−5)

a20 = 253 − 95

a = 158

Therefore, 20th term from the last term is 158.

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