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Mathematical skills account for a minimum of 10% of the marks in A-Level Biology. This lesson covers every type of mathematical calculation you may encounter in the Edexcel A-Level Biology (9BI0) examinations, with worked examples and step-by-step solutions.
Percentage calculations appear frequently in biology exams, including percentage change, percentage difference, and percentage error.
Formula:
Percentage change = ((final value - initial value) / initial value) × 100
Worked Example:
A potato cylinder has an initial mass of 2.50 g. After being placed in a sucrose solution for 30 minutes, its final mass is 2.15 g.
The negative sign indicates a decrease in mass.
Exam Tip: Always include the sign (+ or -) in percentage change calculations. A negative value indicates a decrease. If the question asks for 'percentage decrease', you can give the magnitude without the negative sign.
Formula:
Magnification = image size / actual size
This can be rearranged to:
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