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Find the Sum of All Numbers Between 200 and 400 Which Are Divisible by 7. - 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

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APPEARS IN

 NCERT Solution for Mathematics Textbook for Class 11 (2018 (Latest))
Chapter 9: Sequences and Series
Q: 4 | Page no. 199
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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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