Practice Test Discussion

A can do a piece of work in 8 days, B can do it in 10 days and C can do it in 20 days. In how many days an A, B and C together complete the work ?

$3 \frac{7}{11}$ days

$3 \frac{5}{11}$ days

$3 \frac{2}{11}$ days

$3 \frac{9}{11}$ days

None of these

Explanation

According to the question,

In 1 day,

A can complete $\frac{1}{8}$ ^th part of the work

B can complete $\frac{1}{10}$ ^th part of the work

C can complete $\frac{1}{20}$ ^th part of the work

(A+B+C)'s 1 day's work

$= \frac{1}{8} + \frac{1}{10} + \frac{1}{20} = \frac{5 + 4 + 2}{40} = \frac{11}{40}$

∴ (A+B+C) can finish the work in $\frac{40}{11}$ or $3 \frac{7}{11}$ days.

Hence option A is the correct.

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