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Lesson: Data Sufficiency Intermeddiate - 11

Proportions And Step 1 Of The CAT Method For Data Sufficiency

[Page 11 of 21]

Let's apply Step 1 of CAT's Method (focus on the question stem) to these two examples:

  1. What is Susan's average score for history exams this semester?
    If you know the average formula, then you know that type of information you will need to look for in the statements.


    The question stem provides one part of this three-part formula, so the statements will have to provide the average or the other two parts, sum of the terms and number of terms, to be sufficient.
  2. If Susan's average for her first three out of four exams is 85, and her average for the last three out of four exams is 90, what was her score on the first exam?

This one is tricky. How much information would you need to answer the question? Would you need all three of her other scores to determine her first exam score? Translate what you have been given:

To be sufficient, the statements, alone or in combination, would have to provide:

  • exam 1
  • or
  • exam 2 and exam 3
  • or
  • exam 2 and exam 4
  • or
  • exam 3 and exam 4

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