the sum of three consecutive term of an AP is 9 and the sum of their square is 35 find the sum of all numbers between 200 and 400 which are divisible by 7
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Step-by-step explanation:
The numbers lying between 200 and 400 which are divisible by 7 are 203,210,217,...399
∴ The first term, a=203
Last term, a n =399 & Common difference, d=7
Let the number of terms of the A.P. be n.
∴a n
399=a+(n−1)d
⇒399=203+(n−1)7
⇒7(n−1)=196
⇒n−1=28⇒n=29
∴S 29 = 2 29 /2 (203+399)
602)=(29)(301)=8729
Thus, the required sum is 8729
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