This is arithmetic progression based question from Chapter name- Arithmetic Progression
Chapter number- 9
Exercise – 9.4
In this question we have been given the arithmetic progression and we have to find the 12th term from the end of the arithmetic progressions: 3, 5, 7, 9, …. 201
CBSE DHANPAT RAI PUBLICATIONS
Understanding CBSE Mathematics
Class :- 10th
Question no 13 (i)
Given that,
A.P = 3, 5, 7, 9, …. 201
last term is 201
where, a = 3 and d = (5 – 3) = 2
an = 3 + (n – 1)2 = 201
3 + 2n – 2 = 201
2n = 200
n = 100
Hence the A.P has 100 terms.
therefore, the 12th term from the end is same as (100 – 12 + 1)th of the A.P which is the 89th term.
a89 = 3 + (89 – 1)2
= 3 + 88(2)
= 3 + 176 = 179
Hence, the 12th term from the end of the A.P is 179.