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Find the Sum of All Numbers Between 200 and 400 Which Are Divisible by 7. - CBSE (Arts) Class 11 - Mathematics

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Question

Find the sum of all numbers between 200 and 400 which are divisible by 7.

Solution

The numbers lying between 200 and 400, which are divisible by 7, are

203, 210, 217, ­­­­­­­­… 399

∴First term, a = 203

Last term, l = 399

Common difference, d = 7

Let the number of terms of the A.P. be n.

∴ an = 399 = a + (n –1) d

⇒ 399 = 203 + (n –1) 7

⇒ 7 (n –1) = 196

⇒ n –1 = 28

⇒ n = 29

  Is there an error in this question or solution?

APPEARS IN

 NCERT Solution for Mathematics Textbook for Class 11 (2018 to Current)
Chapter 9: Sequences and Series
Q: 4 | Page no. 199
Solution Find the Sum of All Numbers Between 200 and 400 Which Are Divisible by 7. Concept: Arithmetic Progression (A.P.).
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