The infinite sum 1+47+972+1673+2574+.... equals
Explanation:
Let S = 1+47+972+1673+2574+..... (i)
Dividing (i) by 7, we get,
S7=17+472+973+1674+2575+....(ii) Subtracting (ii) from (i)
6S7=1+37+572+773+974+....(iii) Dividing (iii) by 7
6S49=17+372+573+574+...(iv) Subtracting (iv) from (iii)
36S49=1+217+172+173+...=1+2×171-17=1+2767=43
∴36S49=43S=43×4936=4927
Hence, option (c).
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