When you’re in Year 7 Math, calculating percentages can be tricky. People often make simple mistakes that can lead to confusion. This guide will help you see some common errors. It will also give you tips on how to avoid them and improve your understanding of percentages.

Common Mistakes in Calculating Percentages

1. Mixing Up Percentages, Fractions, and Decimals
   A mistake many students make is not knowing how to change percentages into decimals and fractions.
   To change a percentage to a decimal, just divide by 100.
   For example, $25\%$ becomes $0.25$ because $25 \div 100 = 0.25$.

2. Forgetting the Whole Number When Finding a Percentage
   Sometimes, when you need to find a percentage of a number, you might forget to identify the whole number first.
   If you need to find $20\%$ of $50$, remember that $50$ is your whole number.
   The calculation should be $50 \times 0.20 = 10$.

3. Making Mistakes with Percentage Increases and Decreases
   When you are calculating a percentage increase or decrease, make sure to add or subtract the new value from the original amount.
   For example, if the price is $200$ and it goes up by $15\%$, do it like this:

   • First, find $15\%$ of $200$:
     $200 \times 0.15 = 30$
   • Then, add this to the original price:
     $200 + 30 = 230$

   If you forget any of these steps, your answer won’t be correct.

4. Ignoring the Context of the Problem
   Percentages always relate to a specific situation or whole number.
   A mistake happens when students forget the context of their problem.
   For example, if a store has a $30\%$ discount on something that costs $80$, don’t just write down $30$. You need to calculate what that means.
   The correct calculation is $80 \times 0.30 = 24$, which means the final price is $80 - 24 = 56$.

5. Rounding Too Early
   Sometimes, rounding numbers too early can lead to incorrect answers, especially in problems with multiple steps.
   Keep numbers as they are until you reach the final answer.
   For example, for $15\%$ of $67$, do it this way:
   $67 \times 0.15 = 10.05$
   If you round $10.05$ to $10$ too early, your final answer will not be accurate.

Tips to Avoid These Mistakes

• Take It Step by Step: Break down the calculation into smaller parts so you don’t skip anything. Calculate the percentage first, and then apply it to the whole number.
• Check Your Work: Go back and look at each part of your calculation. If you think $30\%$ of $60$ is $15$, double-check! Do this: $60 \times 0.30 = 18$.
• Practice with Different Problems: The more you practice, the better you will get at spotting and avoiding mistakes.

By remembering these common mistakes and using a careful approach, Year 7 students can become more confident in understanding percentages. Happy calculating!