the average of 8 numbers is 20.the average of the first 2 numbers is 31/2 and that of the next 3 is 64/3.If the sixth be less than the seventh and eighth numbers by 4 and 7 respectively.then the 8th numbers is?

• Total =20*8=160
  Now total of first two numbers=31/2*2=31
  Total of next 3 numbers=64/3*3=64
  Total of first five number=64+31=95
  Let sixth number be x
  Than 7th number is x+4
  8th number will x+7
  Now (95+x+x+4+x+7)/8=20
  106+3x=160
  x=54/3=18
  Therefore 8th no. will be x+7=18+7=25
• 5 years agoHelpfull: Yes(3) No(0)
• let's eight number is a1,a2,a3,a4,a5,a6,a7,a8
  given average of 8 number is = 20
  so a1+a2+a3+a4+a5+a6+a7+a8=20*8=160...........(1)
  then average of the first 2 number is = 31/2
  so a1+a2=31
  then next 3 is = 64/3
  a3+a4+a5=64
  then
  a6=a7-4 and a6=a8-7
  on solving above two equations,we find
  a7=a8-3
  on putting all value exept a8 in equations 1
  then we find a8=25
• 4 years agoHelpfull: Yes(1) No(0)
• Since avg of 8 number is 20.
  Total sum = 8*20=160.
  now it is given that avg of 1st and 2nd number is 31/2 and 3rd,4th,5th number is 64/3.
  It means sum of number from 1 to 5 is 31+64=95.
  now let 8th number be x , then 7th number be x-3 , and 6th number will be x-7 .
  hence total sum = 95+(x-7)+(x-3)+(x)=160
  it gives x=25.
• 5 years agoHelpfull: Yes(0) No(0)
• The sum of first five no will be = 31+64 = 95
  
  Now to have an average of 20 , sum of 8 numbers will be = 160
  
  Let sixth , seventh and eighth no be a , a+4 , a+7 respectively
  
  Now
  
  a + (a+4)+(a+7) = 160-95
  
  So a= 18
  
  So 8th no = (a+8) = 25
• 3 years agoHelpfull: Yes(0) No(0)