Question 1145363
Go to a z-table and find the value closest to 0.64. The z-score that corresponds to this is 0.36.  (NOTE: the z-score of 0.36 has nothing to do with the upper value of 36%.  This is just a coincidence.)
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{{{(x - 68.8)/2.31}}} = 0.36
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Cross-multiply:
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x - 68.8 = 0.8316
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x = 69.6316
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So, the lower 64%/upper 36% point is 69.6 inches.