The average age of 10 students in a group increases by 0.4 years when a girl of age 6 years is replaced by another girl. The age of the new girl is
16.4 yrs
10 yrs
12 yrs
16 yrs
20 yrs

• Let initial average =x
  
  Sum of ages of 10 students of initial group =10x
  Sum of ages of replaced group = 10*(x+0.4) = 10x+4
  
  so age of new girl is 4 years more than girl of 6 yrs.
  so age of new girl = 6+4=10 years.
• 11 years agoHelpfull: Yes(11) No(2)
• The average age of 10 students = (Sum of the age of 10 students)/10
  A = x/10 ---(1)
  when a girl of age 6 years is replaced by another girl.
  Another girl age is y.
  Then,
  New average age is,
  (A+0.4) = (x-6+y)/10
  Solving,
  (x/10)+0.4= (x-6+y)/10
  (x+4)/10 = (x-6+y)/10
  (x+4)= x-6+y
  y = 10 years
  The age of the new girl is 10 Years.
• 11 years agoHelpfull: Yes(2) No(3)
• 11
  
  initial => x / 10 = y
  After => (x - 6 + m)/10 = y + 0.5
  
  Solving both , m = 11 years
• 11 years agoHelpfull: Yes(1) No(10)
• 10*0.4=4
  4*6=24,
  24-4=20years
• 11 years agoHelpfull: Yes(0) No(2)