Dr.sabbir and Eng. Ferdous can finish a certain job in 10 min and 15 min respectively. They started work together but after 2 min manum joined with them . It takes 2 min more to finish the job. If Mamun work alone how many minutes he needs to complete the job????

• 6 minutes
  
  *I think question should be when Mamum joins," it takes 2 min less to finish the job" (Because more men --> less time)
  
  1 min. job of Sabbir and Ferdous= 1/10 + 1/15 = 1/6 => Sabbir and Ferdous can complete the job in 6 min. So their 2 min work= 2*1/6= 1/3
  Let Mamun alone can finish the job in 'x' min.
  After Sabbir and Ferdous's 2 min work, working together all three will complete the job in remaining 2 min (As it requires total 4 min i.e. 2 min less than the 6 min)
  So 2 min's Sabbir and Ferdous's work + 2 min's Sabbir and Ferdous and Mamun work will complete the job. => 1/3 + 2*(1/6 + 1/x) = 1
  => 1/x = 1/6 or x=6
• 7 years agoHelpfull: Yes(2) No(0)
• Dr do work in 1 min=1/10
  Engineer do work in 1 min=1/15
  They work together for 2 min=((2/10)+(2/15))^-1=3
  After 2min manum join them
• 7 years agoHelpfull: Yes(0) No(1)