A contractor hires 100 men to finish a job in 50 days. After 20 days, n men leave. After some more days, the contractor hires 2n more men to complete the job on time. For how many days did these 2n men work?
Choose the most appropriate option:  A) 20  B) 18  C) 15  D) 12  E) 8
Step1: Find Each day what % of work is finished ; it requires 50 days to complete which means each day 1/50= 2% work will be completed.   Step 2 : After 20 Days = 20* 2= 
<gadget id="calculator">20* 2</gadget>
<output>40</output>
40% of work is finished. remaining is 60% ( which means if same 100 men were about to complete the job they would have required 30 more days)   Step3: Let us assume all people have left job. therefore contractor hires 2n people. initially it was taking 30 days to compete for n people. at present 2n people are present to finish job. hence 15 more days.   15
<result>C</result>
A contractor hires 100 men to finish a job in 50 days. After 20 days, n men leave. After some more days, the contractor hires 2n more men to complete the job on time. For how many days did these 2n men work?