Question 972356
A mother has seven children. The mean age of the children is 13years 2months.
 If the mothers age is included , the mean age rises to 17years 7months. 
 Calculate the age of the mother 
:
Convert the mean age of the children to yrs; 13 + {{{2/12}}} = 13.167 hrs
Convert the mean age when mom is included to yrs: 17 + 7/12 = 17.583
:
let m = age of Mom
{{{((7(13.167) + m))/8}}} = 17.583
multiply both sides by 8
92.169 + m = 140.664
m = 140.664 - 92.169
m = 48.495 ~ 48 yrs and 6 months is Mom's age
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Another, more exact way, would be to convert all the ages to months, you can check my answer by doing it that way.