Two pipes A and B can fill a tank in 72 hours, B and C can fill it in 120 hours and pipes A and C can fill it in 90 hours. Then the pipe A alone can fill it in?
[A] 150 h
[C] 80 h
[B] 120 h
[D] 90 h

• 2a+2b+2c=1/72+1/120+1/90
  a+b+c=1/60
  a=1/60-1/120=1/120
  =120 hr ans
• 11 years agoHelpfull: Yes(20) No(0)
• (A+B)'s 1 hr work=1/72 So A's 1 hr work=1/72-B
  (B+C)'s 1 hr work=1/120 so C's 1 hr work=1/120-B
  given (A+C)'s 1 hr work=1/90
  so (1/72-B)+(1/120-B)=1/90
  => 8/360-2B=1/90
  => 8/360-1/90=2B
  => 4/360=2B so B's 1 hr work=1/180
  now A+B 1 hr work =1/72
  so A 1 hr work=1/72-1/180
  =3/360
  =1/120
  so A can fill d tank in 120 hrs
  
• 11 years agoHelpfull: Yes(5) No(0)
• rate of 2(A+B+C) = 1/72+1/120+1/90
  rate of A+B+C = 1/144+1/240+1/180
  rate of A = 1/144+1/240+1/180-1/120 = 1/120 cis./hrs. = 120 hrs./cis.
• 10 years agoHelpfull: Yes(1) No(0)
• A+B=72
  B+C=120
  A+C=90 LCM=360
  perday work a+b=5,b+c=3,a+c=4
  A+B+B+C+A+C=2(A+B+C)
  2(A+B+C)=12
  A+B+C=6
  (a+b+c)-(b+c)=a+b+c-b-c=6-3
  a=3 so,totalwork=360
  360/3=120 ANS=120 h
• 10 years agoHelpfull: Yes(1) No(0)
• ans-60
  a+b=1/72
  b+c=1/120
  c+a=1/90
  2(a+b+c)=1/30
  a+b+c=1/60
• 10 years agoHelpfull: Yes(0) No(1)