The weight of a boy was 40 kg. But, it was wrongly measured as 42 kg. Find the error per cent.

Answer

To find the error percentage in the measurement of the boy's weight, we can follow these steps:

### Step 1: Identify the Actual Weight and Measured Weight
- The actual weight of the boy is 40 kg.
- The measured (wrong) weight is 42 kg.

### Step 2: Calculate the Error
- The error is the difference between the measured weight and the actual weight.
- Error = Measured Weight - Actual Weight
- Error = 42 kg - 40 kg = 2 kg

### Step 3: Calculate the Error Percentage
- The error percentage is calculated using the formula:

\[ \text{Error Percentage} = \left( \frac{\text{Error}}{\text{Actual Weight}} \right) \times 100 \]

- Substituting the values we have:

\[ \text{Error Percentage} = \left( \frac{2 \text{ kg}}{40 \text{ kg}} \right) \times 100 \]

### Step 4: Simplify the Calculation
- First, simplify the fraction:

\[ \frac{2}{40} = \frac{1}{20} \]

- Now, multiply by 100:

\[ \text{Error Percentage} = \left( \frac{1}{20} \right) \times 100 = 5\% \]

### Final Answer
- The error percentage in the measurement of the boy's weight is **5%**.

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