# Arithmetic Progressions

#### Question 4:

How many terms of the AP. 9, 17, 25 … must be taken to give a sum of 636?

#### Answer:

Let there be *n*
terms of this A.P.

For this A.P., *a*
= 9

*d* = *a*_{2}
− *a*_{1} = 17 − 9 = 8

636 = *n *[9 + 4*n*
− 4]

636 = *n *(4*n*
+ 5)

4*n...*

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