Find the sum of all numbers between 200 and 400 which are divisible by 7.
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
Thus, the required sum is 8729.
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10 Comment(s) on this Question
Good
ummma thank you
But how I know that first no. Is 203
thank you great elucidation
wonderfull explanation
Thank you for your help
Good solution.
Thanks for the explanation
it was a wonderful explanation
Good explanation
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