If Sunil takes half as long to do a piece of work as Vimal takes and if Sonu does it in the same time as Sunil and Vimal together. If all three working together would take 7 days, Vimal alone can finish the work in -
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48 days
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42 days
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36 days
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21 days
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None of these
B
Correct answer
Explanation
Let Vimal's time = 2x days. Then Sunil's time = x days (half of Vimal). Sunil + Vimal together: 1/x + 1/(2x) = 3/(2x), so time = 2x/3 days. This equals Sonu's time. All three together: 1/x + 1/(2x) + 3/(2x) = 1/x + 4/(2x) = 3/x. So time = x/3 = 7 days, giving x = 21. Vimal alone = 2x = 42 days.