find the sum of all numbers between 200 and 400 which are divisible by 7.... ?
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find the sum of all numbers between 200 and 400 which are divisible by 7.... ?
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8729is ur answer
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★ Given :
A.P : 203, 210, 21 ........ 399
First term (a) = 203
Common Difference (d) = 7
Last term (An or L) = 399
[tex]\rule{200}{1}[/tex]
★ To Find :
We have to find the sum of all number between 200 and 409 which are divisible by 7.
[tex]\rule{200}{1}[/tex]
★ Solution :
We know that,
An = a + (n - 1)d
→ 399 = 203 + (n - 1)7
→ 399 - 203 = (n - 1)7
→ 196 = (n - 1)7
→ n - 1 = 196/7
→ n - 1 = 28
→ n = 28 + 1
→ n = 29
[tex]\rule{200}{2}[/tex]
Sn = n/2 (a + L)
→ Sn = 29/2 (203 + 399)
→ Sn = 29/2 * 602
→ Sn = 29 * 301
→ Sn = 8729