the average age of four boys,five years ago was 9 years.On including a new boy,the present average age of all the five is 15 years.the present age of the new boy is..

• Ans=19 years
  Total present age of four boys=4*9+4*5=56 years
  If present age of the new boy=x & total present age of 5 boys=15*5=75
  then 56+x=75 =>x=19 years
• 11 years agoHelpfull: Yes(3) No(0)
• The average age of four boys,five years ago was 9 years.
  The Present average age of four boys = 9 years + 5 Years = 14 Years
  On including a new boy,
  The present average age of all the five is 15 years.
  The present age of the new boy =
  (Sum of the present age all the 5 boys - sum of the present age of 4 boys)
  = 5*15 - 4*14
  = 75 -56
  = 19years
  
  
• 11 years agoHelpfull: Yes(1) No(0)
• before 5 years avrg age=5.
  
  total/4=5 => total=20.
  
  after 9 years each one(4 boys) increase years by 9, and add one new boy.
  (20+4*9+new boy age)/5=15.
  56+ new boy age=75
  new boy age=19.
• 11 years agoHelpfull: Yes(1) No(0)