today question date 16 sep 2016

1 if A and B work together , they will complete a job in 7.5days.however,
if A works alone and completes half of the work and then B takes over and
complete the remaining half alone, they will take 20days
.how long will B alone takes to do the work if A is more efficient than B?

ans 30

2 .In how many different ways can 5 girls and 5 boys form a circle such that the boys and the girls alternate?

Options
1) 2880
2) 1400
3) 1200
4) 32

• five girls can be seated in circle in (5-1)! ways=4!=24
  remaining boys can be placed in 5! ways=120
  total ways =120*24=2880
• 8 years agoHelpfull: Yes(16) No(0)
• 2) After fixing one girl, the remaining 4 girls can sit in 4! Ways.
  Since boys and girls have to alternate, there will be 5 places, one place each for boys in between the girls. These 5 places can be filled by 5 boys in 5! Ways.
  So, the required no.of ways = 5!*4!
  = 5*4*3*2*1*4*3*2*1
  = 2880 ways
• 8 years agoHelpfull: Yes(15) No(1)
• 10 days
  
  (1/A)+(1/B)= 2/15 ----(i) and (1/2)/(1/A) + (1/2)/(1/B) = 20 ----(ii)
  From (ii), (A/2) + (B/2)= 20 or A+B=40
  As we require B, substitute A=40-B in (i), we have 1/(40-B) + (1/B)= 2/15
  => B^2 -40B +300=0
  => (B-10)(B-30)=0 , B= 30 or 10
  As A+B=40 and A is more efficient than B, so A=30 and B=10
• 8 years agoHelpfull: Yes(10) No(8)
• 5 girls can be arranged in a circle as = 4!
  remaining 5 boys can be arranged at 5 places (one place between any two consecutive girls)= 5!
  combining both final answer= 4! * 5! = 2880
• 8 years agoHelpfull: Yes(2) No(0)
• 5!*5!=1400
• 8 years agoHelpfull: Yes(0) No(23)
• 5!*4!=2880
• 8 years agoHelpfull: Yes(0) No(0)
• 5!*4!
  2880
• 7 years agoHelpfull: Yes(0) No(0)
• After fixing one girl, the remaining 4 girls can sit in 4! Ways.
  Since boys and girls have to alternate, there will be 5 places, one place each for boys in between the girls. These 5 places can be filled by 5 boys in 5! Ways.
  So, the required no.of ways = 5!*4!
  = 5*4*3*2*1*4*3*2*1
  = 2880 ways
• 6 years agoHelpfull: Yes(0) No(0)