Question 1098951
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Shortly speaking, the problem says that one third of the mother's age minus one fourth of the mother's age is 3.


Or, in the symbolic form,

{{{(1/3)*M - (1/4)*M}}} = 3.


To solve it, multiply both sides by 12. You will get

4M - 3M = 3*12,   or  M = 36.


<U>Answer</U>.  Mother is 36 years old. Nathan is 9 years old. His sister is 12 years old.
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Solved.