Question

a can do a work in 15 days and b in 20 days. if they work on it together for 4 days, then the fraction of the work that is left is : a. 1/4 b. 1/10 c. 7/15 d. 8/15

Answer 1

$<b><i>$Time taken by A = 15 days


A's 1 day's work =1/15


Time taken by B = 20 days


B's 1 day's work =1/20


$(A + B)'s \: \: 1 \: day's \: \: work = \frac{1}{15} + \frac{1}{20} \\ \\ = \frac{4+ 3}{60} \\ \\ = \frac{7}{60}$

$(A + B)'s \: \: 4 \: day's \: \: work = \frac{7}{60} \times 4 \\ \\ = \frac{7}{15}$

$Therefore, \: Remaining \: work =1 - \frac{7}{15} \\ \\ = \frac{15 - 7}{15} \\ \\ = \frac{8}{15}$

d) So clearly option d) will be the correct answer


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