Classifying a group into two different ways

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SUMMARY

The discussion centers on a mathematical problem from an SAT math study guide regarding the classification of students into seniors and juniors. The ratio of seniors to juniors is established as 4:5, leading to the conclusion that 4/9 of the group are seniors and 5/9 are juniors. The confusion arises from the addition of fractions A + B equating to 4/9, which is clarified through the understanding of how to combine fractions to represent parts of a whole. The key takeaway is the importance of understanding ratios and fractions in solving classification problems.

PREREQUISITES
  • Understanding of basic fractions and ratios
  • Familiarity with SAT math concepts
  • Ability to perform arithmetic operations with fractions
  • Knowledge of percentage calculations
NEXT STEPS
  • Study the concept of ratios in depth
  • Learn how to add and subtract fractions effectively
  • Explore the relationship between fractions and percentages
  • Practice SAT math problems focusing on classification and grouping
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Students preparing for the SAT, educators teaching math concepts, and anyone looking to improve their understanding of ratios and fractions in mathematical contexts.

Aaron H.
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I don't understand this example. It's from an SAT math study guide. I understand that to find the fraction of the group that is both girls and seniors, 2/3 is multiplied times 2/5. Why is A + B equal to 4/9? Same with A + C.
 
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Why is A + B equal to 4/9?

As the problem tells you, the ratio of seniors to juniors is 4:5. If there are 9 students, then 4/9 are seniors and 5/9 are juniors.
 
Thanks. I had thought of that but I wasn't sure about it. So I guess the idea here is to, when given a fraction for a group, find the fraction that when added would make the sum of the two a whole number. Fractions are decimal numbers, after all. Percentages come to mind as well.
 

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