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Which Term of A.P 3, 10, 17, .... Will Be 84 More than Its 13th Term? - Mathematics

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Question

Which term of A.P 3, 10, 17, .... Will be 84 more than its 13th term?

Sum

Solution

The given A.P is 3, 10, 17, ....

Here a = 3, and d = 10 - 3 = 7

Now

`t_13 = a + 12d = 3 + 12 xx 7 = 3 + 84 = 87`

Let the required term be nth term

`:. t_n - t_13 = 84`

=> [a + (n - 1)d] - 87 = 84

`=> 3 + (n - 1) xx 7  = 171`

`=> (n - 1) xx 7  = 168`

=> n - 1 = 24

=> n = 25

Thus required term = 25th term

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Arithmetic Progression - Finding Their General Term
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Chapter 10: Arithmetic Progression - Exercise 10 (B) [Page 140]

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Selina Mathematics [English] Class 10 ICSE
Chapter 10 Arithmetic Progression
Exercise 10 (B) | Q 16 | Page 140
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