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The actual dimensions of a rectangle are 
9cm by 
10cm. Alex measures the sides to be 
8.65cm by 
10.29cm. In calculating the area, what is the relative error, to the nearest thousandth.
Answer:

The actual dimensions of a rectangle are 9 cm 9 \mathrm{~cm} by 10 cm 10 \mathrm{~cm} . Alex measures the sides to be 8.65 cm 8.65 \mathrm{~cm} by 10.29 cm 10.29 \mathrm{~cm} . In calculating the area, what is the relative error, to the nearest thousandth.\newlineAnswer:

Full solution

Q. The actual dimensions of a rectangle are 9 cm 9 \mathrm{~cm} by 10 cm 10 \mathrm{~cm} . Alex measures the sides to be 8.65 cm 8.65 \mathrm{~cm} by 10.29 cm 10.29 \mathrm{~cm} . In calculating the area, what is the relative error, to the nearest thousandth.\newlineAnswer:
  1. Calculate Actual Area: Calculate the actual area of the rectangle using the actual dimensions.\newlineThe formula for the area of a rectangle is length×width\text{length} \times \text{width}.\newlineActual area = 9cm×10cm=90cm29\,\text{cm} \times 10\,\text{cm} = 90\,\text{cm}^2.
  2. Calculate Measured Area: Calculate the measured area of the rectangle using the measured dimensions.\newlineMeasured area = 8.65cm×10.29cm8.65\,\text{cm} \times 10.29\,\text{cm}.\newlineLet's perform the multiplication to find the measured area.\newlineMeasured area = 89.0055cm289.0055\,\text{cm}^2.
  3. Calculate Absolute Error: Calculate the absolute error by subtracting the actual area from the measured area.\newlineAbsolute error = Measured areaActual area|\text{Measured area} - \text{Actual area}|.\newlineAbsolute error = 89.0055cm290cm2|89.0055\text{cm}^2 - 90\text{cm}^2|.\newlineAbsolute error = 0.9945cm2|-0.9945\text{cm}^2|.\newlineSince we are looking for the absolute value, we take the positive value.\newlineAbsolute error = 0.9945cm20.9945\text{cm}^2.
  4. Calculate Relative Error: Calculate the relative error by dividing the absolute error by the actual area.\newlineRelative error = Absolute errorActual area\frac{\text{Absolute error}}{\text{Actual area}}.\newlineRelative error = 0.9945cm290cm2\frac{0.9945\,\text{cm}^2}{90\,\text{cm}^2}.\newlineLet's perform the division to find the relative error.\newlineRelative error 0.01105\approx 0.01105.
  5. Convert Relative Error: Convert the relative error to the nearest thousandth.\newlineTo convert to the nearest thousandth, we round the relative error to three decimal places.\newlineRelative error 0.011\approx 0.011.

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