Question

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

Answer 1

Hint: First, we will find how much is 25% of 72kg using the formula \[b\%\times a\] . Then we will subtract that answer from 72kg as it is told that the wife's weight is less than man. Then we will find 10% of the wife's weight using the same formula and will add to the wife's weight because it is told that the son's weight is 10% more than the wife. Thus, we will get the weight of our son.

Complete step-by-step answer:
Here, we are given a weight of 72 kg. Now, his wife's weight is 25% less than his. So, we will find how much is 25% of 72 using the formula \[b\%\times a\] where a is 72 and b is 25%.
On substituting the values, we get as
\[\dfrac{25}{100}\times 72\]
On solving, we get as
\[\dfrac{1}{4}\times 72=18\]
So, 25% of 72 is 18. So, now subtracting it from man’s weight, we get weight of wife as
\[72-18=54kg\] ……………………(1)
Now, it is said that a son's weight is 10% more than his wife. So, first we will find 10% of 54 using the same formula i.e. \[b\%\times a\] . On substituting the values, we get as
\[\dfrac{10}{100}\times 54=5.4kg\]
Now, 5.4 is 10% of 54. Son’s weight is 10% more than the wife's, so we will add 5.4 to wife 's weight. Thus, we get as
\[5.4+54=59.4kg\] …………………(2)
Thus, my son's weight is 59.4kg.

Note: Another way for directly finding how much is 25% of 72 is by using the formula \[\left( a-b\%\cdot a \right)\] . If less word is there then minus sign will come in equation, else more word is there then plus sign will come in equation i.e. \[\left( a+b\%\cdot a \right)\] . So, by this we get wife’s weight as \[\left( 72-\dfrac{25}{100}\cdot 72 \right)=54kg\] and for son’s weight we get same answer as \[\left( 54+\dfrac{10}{100}\cdot 54 \right)=59.4kg\] . So, the answer will remain the same.