to do certain work alone 'A' takes 4 hrs,'B' takes 5 hrs and c takes 6 hrs.how long would A and b together take to do a work which C can do in 4 n half hours?

• A and B together does 9/20th of the work in an hour. C alone does 1/6th of the work in an hour. so in 4.5 hours C does 4.5/6th of the work. time required for A and B to do the same work is {(4.5/6)/(20/9)}=5/3hours.
• 7 years agoHelpfull: Yes(20) No(0)
• RATE * TIME = WORK
  A 30 4 120
  B 24 5 120
  C 20 6 120
  
  AS L.C.M OF 4,5,6 is 120 rates can be found out easily
  now
  c's 4.5 hrs of work = (A+B)'s of work
  20*2.5=(30+24)*Time (r*t=w)
  Time taken by A & B =5/3 hrs
• 7 years agoHelpfull: Yes(5) No(0)
• 5/3 hours is the right answer
• 7 years agoHelpfull: Yes(3) No(0)
• C do the work in 4.5/6 hrs = 3/4 (Total work)
  A do that work in 3/4 * 4 = 3
  B do that work in 3/4 * 5 = 3.75
  Therefore A and B do the work in x/ 3 + x / 3.75 = 1
  x = 1 2/3 hrs
• 7 years agoHelpfull: Yes(2) No(0)
• A's one hour Work=1/4
  B's one hour work=1/5
  C's one hour work=1/6
  let us consider A and B together work by x hours
  so
  (x/4)+(x/5)+(9/2*6)=1
  x=5/9
  so total time taken by A & B is 9/5.
• 7 years agoHelpfull: Yes(1) No(13)
• 23/15 hours. as the amount of work done is 3/4 by c in 4.5 hours
  
• 7 years agoHelpfull: Yes(0) No(15)
• my answer is 3 and half hours
• 4 years agoHelpfull: Yes(0) No(0)