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. Also we have to find Which term of the AP 21. 42, 63, 84, … is 420
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Understanding CBSE Mathematics
Class :- 10th
Question no 2(iv)
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Question 2. Find: (iv) Which term of the AP 21. 42, 63, 84, … is 420?
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Given that,
A. P 21, 42, 63, 84, ………
a = 21,
nth term = 420,
d = a2 – a1
= 42 – 21 = 21
As we know that, to find nth term in an A.P = a + (n – 1)d
21 + (n – 1)21 = 420
(n – 1)21 = 399
n – 1 = 399/21 = 19
n = 20
Hence 20th term is 420.