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Engineering

Let $S_n$ denote the sum of the first n terms of an arithmetic progression. If $S_{10} = 390$ and the ratio of the tenth and the fifth terms is 15 : 7, then $S_{15} - S_5$ is equal to:

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A metal wire of uniform mass density having length L and mass M is bent to form a semicircular arc and a particle of mass m is placed at the centre of the arc. The gravitational force on the particle by the wire is: [Diagram: Semicircular arc with mass m at center]

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Questions

Questions

Let SnS_nSn​ denote the sum of the first n terms of an arithmetic progression. If S10=390S_{10} = 390S10​=390 and the ratio of the tenth and the fifth terms is 15 : 7, then S15−S5S_{15} - S_5S15​−S5​ is equal to:

Related questions

Let $S_n$ denote the sum of the first n terms of an arithmetic progression. If $S_{10} = 390$ and the ratio of the tenth and the fifth terms is 15 : 7, then $S_{15} - S_5$ is equal to: