From the study guide Find the mistake: fractions and percentages
Study guide for Grades 5 to 8: preserve the value and use the right whole; 2 worked examples and 4 practice questions. Equivalent fractions require multiplying or dividing numerator and denominator by the same nonzero number.
Preserve the value: Equivalent fractions require multiplying or dividing numerator and denominator by the same nonzero number.
Use the right whole: A percentage comparison changes when the reference whole changes.
Example: Correct 1/3 + 1/4 = 2/7 and explain. Answer: Use a common denominator: 4/12 + 3/12 = 7/12. Adding denominators is not the addition rule..