The mean +/- 0.67 standard deviations cuts off 25% in each tail of the Normal distribution. Hence…

The mean +/_ 0.67 standard deviations cuts off 25% in
each tail of the Normal distribution. Hence the middle 50% of the distribution
lies within +/_ 0.67 standard deviations of the mean. Use this fact to
calculate the inter-quartile range for the distribution x ~ N(200, 256).