Question

20 men can do a piece of work in 18 days. They worked together for 3 days, then 5 men joined. In how many days is the remaining work completed?


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Answer 1

20 men=18 days

=work done by 20 men working

together =1 work

=work done by them in 3 days working

$together = 1 \times 3 = 3$

$remaining \: work = 18 - 3 = 15 \: work$

15 work to be done

$(20 + 5 = 25men)$

efficiency of 20 men = 1

$efficiency \: of \: 1 \: men = \frac{1}{20}$

$efficiency \: of \: 5 \: men = \frac{5}{20} = \frac{1}{4}$

$so \: effeciency \: of \:( 20 + 5)$

$25men = \frac{5}{4} working \: days$

$required \: time = \frac{work}{effeciency} 15 \div 5 \div 4 = 12days$

therefore 12 days more will be taken to complete the work