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Question: Answered & Verified by Expert
Let a1, a2, a3,  be an A.P. If a1+a2++a10a1+a2++ap=100p2, p10, then a11a10 is equal to :
MathematicsSequences and SeriesJEE MainJEE Main 2021 (31 Aug Shift 2)
Options:
  • A 1921
  • B 100121
  • C 2119
  • D 121100
Solution:
2149 Upvotes Verified Answer
The correct answer is: 2119

Given, a1+a2++a10a1+a2++ap=S10Sp=100p2

1022a1+9dp22a1+p-1d=100p2

102a1+9dp2a1+p-1d=100p2

2a1+9d2a1+p-1d=10p

Let, a1=a

2pa+9pd=20a+10pd-10d

2pa-20a=pd-10d        

2ap-10=dp-10

2a=d

ad=12

Now, a11a10=a+10da+9d

a11a10=dad+10dad+9

a11a10=12+1012+9

a11a10=2119

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