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A man weighs 72kg. His wife's weight is 25% less than his, if their son weighs 10% more than his mother. Find the son’s weight.

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Hint: The weight of the man is given in the question and the relation between his weight and his wife is also provided, a relation between his wife’s age and his son’s weight is also given. Thus this means that an indirect relation between his son’s weight and his weight can be formulated. Assume his wife’s weight to be variable. Use these relations to formulate mathematical equations so that the value of this variable could be taken out hence the weight of his son could be formulated.

Complete step-by-step answer:
Given data
The weight of a man is 72 kg.
The weight of his wife is 25% less than his.
Let the weight of the wife be x kg.
Now construct the linear equation according to given information.
I.e. The weight of a wife is equal to the weight of man minus 25% weight of man.
I.e. x is equal to 72 minus 25% of 72.
$ \Rightarrow x = 72 - \dfrac{{25}}{{100}}\left( {72} \right)$
Now simplify the above equation we have,
$ \Rightarrow x = 72 - \dfrac{1}{4}\left( {72} \right) = 72 - 18 = 54$ Kg.
Now it is given that his son weighs 10% more than his mother.
Let the weight of the son be y kg.
Now construct the linear equation according to given information.
I.e. The weight of the son is equal to the weight of mother plus 10% weight of mother.
I.e. y is equal to 54 plus 10% of 54.
$ \Rightarrow y = 54 + \dfrac{{10}}{{100}}\left( {54} \right)$
Now simplify the above equation we have,
$ \Rightarrow y = 54 + \dfrac{1}{{10}}\left( {54} \right) = 54 + 5.4 = 59.4$ Kg.
So, the weight of the son is 59.4 kg.
So, this is the required answer.

Note: Whenever we face such types of problems the key point is to formulate mathematical equations using the information provided in the question. This helps in taking out the value of the unknowns and thus we can get the required entity asked in the question.