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**Hint**: In the class, children comprise both the girls and boys. If the percentage of girls are given then subtracting it from the number hundred we get the percentage of boys. Simply find the percentage of boys for the total children in the class.

**:**

__Complete step-by-step answer__Given that: In a class of $ 60 $ children, $ 30\% $ are girls

Class has both the girls and the boys.

Boys $ \% = 100\% - 30\% $

Simplify finding the difference of the terms in the above expression –

Boys $ \% = 70\% $

Now, the number of boys $ = 70\% $ of the total children

Here “of” suggests the multiplication operator.

the number of boys $ = 70\% \times 60 $

percentage is expressed as the number upon hundred. So, place $ 70\% = \dfrac{{70}}{{100}} $ in the above expression –

The number of boys $ = \dfrac{{70}}{{100}} \times 60 $

Find the factors for the above expression –

The number of boys $ = \dfrac{{7 \times 10 \times 6 \times 10}}{{10 \times 10}} $

Common factors from the numerator and the denominator cancel each other and therefore remove from the numerator and the denominator of the above expression.

The number of boys $ = 7 \times 6 $

Simplify finding the product of the terms in the above expression –

The number of boys $ = 42 $ Boys

Hence, there are $ 42 $ boys in a class.

**So, the correct answer is “42”.**

**Note**: The above example can be used by finding the percentage given of girls in number of girls and then have to subtract the number of girls from the total number of children to get the number of boys since the class contains boys and girls. Always convert the given percentage in the form of the fraction where the numerator is hundred.

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