Question

Mrs. Bennett has graded $20\% $ of her $150$ student’s papers. How many papers does she still need to finish grading?

Answer 1

Hint: In this question, it is given that Mrs. Bennett has graded $20\% $ of her $150$ student’s papers and asked us to find how many she still needs to finish. If $20\% $ of her $150$ student’s papers is finished, then the remaining will be $80\% $ of her $150$ student’s papers. So we need to find $80\% $ of $150$to find the answer.

Formulas used:
Percentage= $\dfrac{{{\text{part}}}}{{{\text{whole}}}} \times 100$
Part = ${{whole \times }}\dfrac{{{\text{percentage}}}}{{{\text{100}}}}$

Complete step by step answer:
In this question, it is given that Mrs. Bennett has graded $20\% $ of her $150$ student’s papers and asked us to find how many she still needs to finish.
Clearly there are $150$student’s papers that are to be graded.
Among these $150$ student’s papers, $20\% $ of them are graded. Therefore the number of papers graded is $150{\text{ of }}20\% $.
That is, $150{\text{ of }}20\% $
$ \Rightarrow 150 \times \dfrac{{20}}{{100}}$
Multiplying the terms, we get
$ \Rightarrow \dfrac{{3000}}{{100}}$
Cancelling the zeros,
$ \Rightarrow 30$
Hence, $30$ student’s papers are graded.
There are a total of $150$ student’s papers, among them $30$ of them are graded then the remaining papers i.e., the number of papers that are still needed to be graded are $150 - 30$.
$ \Rightarrow 120$

Therefore $120$ student’s papers are still to be graded.

Note: Alternative way to find the answer is,
There are $150$ student’s papers and $20\% $ of them are graded.
Thus among $100\% $ ,$20\% $ is over. Therefore the remaining is $80\% $
Then we need to $80\% $ of total papers to find the number of papers that are yet to be graded.
i.e.${\text{ 80% of }}150{\text{ }}$
$ \Rightarrow 150 \times \dfrac{{80}}{{100}}$
On cancel the terms and we get,
$ \Rightarrow 15 \times 8$
On multiply we get,
$ \Rightarrow 120$
Therefore $120$ student’s papers are still to be graded.