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Question
An Arithmetic Progression (A.P.) has 3 as its first term. The sum of the first 8 terms is twice the sum of the first 5 terms. Find the common difference of the A.P.
Solution
a = 3,
`\implies` S8 = 2S5
`\implies 8/2[2 xx 3 + (8 - 1)d] = 2{5/2[2 xx 3 + (5 - 1)d]}`
`\implies` 4[6 + 7d] = 5[6 + 4d]
`\implies` 24 + 28d = 30 + 20d
`\implies` 8d = 6
`\implies` d = `3/4`
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