Q&A for How to Calculate Percentage Error

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In a resistor, the relationship between the voltage V, the current I and resistance R, is given by Ohm's law: V=IR. If the voltage is constant, how is the relative change in R related to the relative change in the current?

Donagan

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I and R are inversely proportional. That means that as I increases, R decreases by the same percentage (and vice versa).

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Do I use significant figures while calculating percentage error?

Donagan

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Yes.

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How do I calculate the percentage error in the kinetic energy of a particle?

Community Answer

Multiplying the relative errors of measuring the mass and the velocities should do.

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How do I find the percentage error when the numerator is going to be a negative?

Donagan

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The sign of the numerator doesn't matter. It has no effect on the percentage.

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What happens if my exact value is less then my theoretical value? Is there such thing as a negative percent error?

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If it is less than the true value, the percent error will be negative. If it is greater than the true value, the percent error will be positive.

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How do I calculate a percentage error when resistors are connected in a series?

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Carry the 2 and get the square root of the previous answer.

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How do I find the percent error in an experiment with three trials?

Community Answer

Find the average percentage of your three trials. You can do this by finding the percent of each trial, adding them all together, and then dividing it by the number of trials (which, in this case, is 3). Use that average in your calculation to find the percent error.

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How do I calculate percentages?

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Divide the amount you have by the total amount possible, then multiply by 100. E.g. If you have 5 apples and there are 20 apples altogether, then you have 5/20=0.25*100=25% of the apples.

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Question

A number, 5.7810101, is wrongly written as 5.9810101. What is the percentage of error?

Donagan

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The error is 5.981 - 5.781 = 0.2. 0.2 / 5.781 = 0.034596, so the percentage of error is 3.4596%.

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How do I calculate the percentage error when more than one result is obtained?

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You can choose to sum up the results, or do the results separately, then count the average of the error percentage.

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After solving it, will the answer be in a percentage?

Donagan

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Yes. You'll first get a fraction, which can be converted to a decimal, which should be multiplied by 100 to get a percentage.

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In a population of 1500 students that was wrongly recorded as 900, find the percentage error?

Donagan

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(1500 - 900) / 1500 = 600 / 1500 = 2/5 = 0.4 = 40%.

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A surveyor measured a road as been 69.3km. However, there is a -1% error in the measurement. What is the true length of the road?

Donagan

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A -1% error means that you would take 1% of the measured length and add it to the measured length to find the true length: 69.3 + 0.693 = 69.993 km (or 70.0 km if you want to use just one decimal digit).

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How do I calculate the percent error if my theoretical value is 0?

Donagan

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Generally that would not be possible, because the suggested "theoretical value" has no value at all and thus is not measurable. (One case where it could work is temperature, but the actual and estimated values would have to be converted first to the Kelvin scale.)

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How do I know which number is the exact and approximate?

Donagan

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The "exact" number is the known (correct) number. The "approximate" number is the incorrectly measured (or the estimated) number.

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How do I calculate relative error?

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See Calculate Relative Error .

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If the age of a man who is 64 years is written as 71 years, calculate the percentage error in 3 significant figures?

Donagan

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The error is 71 - 64 = 7 years. The percentage of error is 7/64 = 0.109 = 10.9%.

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A sales girl gave a change of 1.15 to a customer instead of 1.25, what is the percentage error?

Donagan

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The error is 1.25 - 1.15 = 0.10. The percentage of error is 0.10 / 1.25 = 0.08 = 8%.

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How to get an percentage in piegraph?

Donagan

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Let's assume the percentage being shown is between 0% and 100%. First show the percentage as a fraction with a denominator of 100. For example, 39% = 39/100. Now set up an equation with that fraction equaling x/360°, where x is the central angle representing the indicated percentage of the pie. In this example, the equation is 39/100 = x/360°. Cross-multiply to solve for x: (39)(360°) = (100)(x). So 14040° = 100x, and x = 140.4°. Use a protractor to mark off a central angle of 140.4° in a pie.

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Can my final answer while calculating percentage error be negative?

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Only when your experimental value is negative as the numerator will always be positive (Positive divided by negative is negative).

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