obama is a creator and osama is a destroyer. if obama dis any work in 21 months and osama did it in 28 months. in how many months they did the work complete if they are working alternatively.

• 161 months
  
  creator 1/21 of a building in a month
  destroyer 1/28 of a building in a month
  
  in two months (1/21)-(1/28)=1/84
  in one month building completed = 1/168
  
  They are working alternatively so first creator creates a building and the destroyer destroys it in the next month)
  
  If building completed in 1 month = 1/168
  then in 160 month building completed = 160/168
  
  now the 161 month is creators turn so 160/168 + 1/21=168/168
  
  Hence in the 161 month building will be completed.
• 10 years agoHelpfull: Yes(38) No(2)
• ans 161
  
  a works 588/21=28unit/month
• 10 years agoHelpfull: Yes(4) No(2)
• 168 months
• 10 years agoHelpfull: Yes(1) No(3)
• Let total work=84 units (lcm of 21 and 28)
  So obama works or creates = 84/21=4 units per month,
  and osama works or destroys= 84/28=-3 units per month.(osama is destroyer so negative sign taken.)
  So net work will be = 4-3=1.
  
  
  
• 10 years agoHelpfull: Yes(0) No(4)
• 168 months
  
• 10 years agoHelpfull: Yes(0) No(0)