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In a test of $ 30 $ questions Peter answers $ 80\% $ of them correctly. Find the number of incorrect answers.

Answer
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Hint: Since it is given that Peter answers $ 80\% $ of them correctly so from this it means that $ 20\% $ of them will be incorrect and from this, we can now easily calculate the number of incorrect answers by solving the equation $ 20\% $ of total questions.

Complete step-by-step answer:
As in this question it is given that there are a total of $ 30 $ questions and out of which Peter answers $ 80\% $ of them correctly. So we have to find the number of incorrect answers.
For this, we will calculate the incorrect answer percentage,
Therefore, the incorrect answer percentage will be,
 $ \Rightarrow 100\% - 80\% $
And on solving it we get
 $ \Rightarrow 20\% $
Since $ 20\% $ of the answers are incorrect, the number of questions which are incorrect will be calculated by $ 20\% $ of total questions.
Mathematically we can write it as
 $ \Rightarrow 20\% {\text{ }} \times {\text{ 30}} $
And on removing the percentage the equation will be
 $ \Rightarrow \dfrac{{20}}{{100}} \times 30 $
And on solving the above equation, we get the value as
 $ \Rightarrow 6 $
Hence, the number of incorrect answers is $ 6 $ .
So, the correct answer is “6”.

Note: In this type of question, there is not much calculation needed. By reading the question carefully and solving it we can easily solve such questions. We should also know that the whole amount of being something will be a hundred percent. Since the percentage is being widely used in reasoning tests so us it becomes important that we understand and interpret them effectively.