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Posted by on Monday, September 17, 2012 at 10:34pm.

A group of 20 preschoolers were tested on reading readiness. The mean on this test is 30.9, with SD=2.08. What percentage of children scored between 25 and 28.5?

  • Statistics - , Tuesday, September 18, 2012 at 4:59pm

    Use z-scores.

    Find two z-scores using this formula:
    z = (x - mean)/sd

    Mean = 30.9
    Sd = 2.08

    Use 25 for x to determine first z-score.
    Use 28.5 for x to determine second z-score.

    Once you have both z-scores, check a z-table for the probability between the two scores. Convert to a percent.

    I hope this will help get you started.

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