You can put this solution on YOUR website! Find the z-score for the standard normal distribution where:
P(z< -a) = 0.2451
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Draw a standard normal curve.
Shade a left-tail area that is 24.51%
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Find the z-value with that left-tail area.
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invNorm(0.2451) = -0.6900
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a = 0.6900
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cheers,
Stan H.