1.

Find the common difference of an AP whose first term is 1 and the sum of the first four terms is one-third to the sum of the next four terms.

Answer» `1,1+d,1+2d,1+3d,1+4d,....`
`1+1+d+1+2d+1+3d=1/3(1+4d+1+5d+1+6d+1+7d)`
`4+6d=1/3(4+22d)`
`12+18d=4+22d`
`d=2`.


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