Question

Average age of 12men is 20 years if age of one more is added to it the average is decreased by one year find out the age of that man

Answer 1

the age of the other man should be 7 as avg will be 247 when added.

Answer 2

Average age of 12men is 20 years if age of one more is added to it the average is decreased by one year find out the age of that man
Solution:
           Sum of ages of 12 men  = average age * number of men
                                               = 20 *12
                                               = 240
       Let the age of newly added man = x
  therefore average age =  sum  of ages of 13 men / number of men
                           19 =  (240 + x ) / 13
                           19*13 = 240+x
                           247 = 240 + x
                         247 - 240 = x
                         7 = x
Therefore the age of the newly added person =  7 years.

Hope this is helpful!!!