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Class A and class B took the same test.

This topic has 1 expert reply and 0 member replies

Class A and class B took the same test.

Post Fri Sep 15, 2017 6:49 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    Class A and class B took the same test. The average (arithmetic mean) score for class A was 79.5. What was the average score for all the students in both classes?

    (1) The average score for class B was 80.5.
    (2) Class B had 25 fewer students than class A.

    The OA is E.

    Can someone help me here? Thanks.

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    Post Fri Sep 15, 2017 7:13 pm
    Vincen wrote:
    Class A and class B took the same test. The average (arithmetic mean) score for class A was 79.5. What was the average score for all the students in both classes?

    (1) The average score for class B was 80.5.
    (2) Class B had 25 fewer students than class A.
    Each statement is clearly insufficient on its own.

    Statements combined:
    To make the math easier, test smaller values for the two averages.
    Let the average score in Class A = 1 and the average score in Class B = 2.

    Case 1: 30 students in Class A with an average score of 1, 5 students in class B with an average score of 2
    Average for all 35 students = (30*1 + 5*2)/35 = 40/35 = 8/7.

    Case 2: 35 students in Class A with an average score of 1, 10 students in class B with an average score of 2
    Average for all 45 students = (35*1 + 10*2)/45 = 55/45 = 11/9.

    Since the average for the two classes can be different values, INSUFFICIENT.

    The correct answer is E.

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    Thanked by: Vincen
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