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# STANDARD DEVIATION MATH HELP?

The average newborn baby weighs 7.9 lbs with standard deviation of approximately 0.5lbs. If this is normal distribution, then what percentage of babies would be more than 9.4 lbs?

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- King LeoLv 71 month ago
z = ( x - µ ) / 𝛔

z = ( 9.4 - 7.9 ) / 0.5

z = 3

accumulative p-value from z-score table where z = 3.00.

From the index table, p = 0.9987

∴ P( X < 7.9 ) = 0.9987

∴

P( X > 7.9 ) = 1 - P( X < 7.9 )

P( X > 7.9 ) = 1 - 0.9987

P( X > 7.9 ) = 0.0013 = 0.13%

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- 1 month ago
(9.4 - 7.9) / 0.5 = 1.5/0.5 = 3

99.7% of data is between -3 and +3 standard deviations from the mean.

100 - (50 + 99.7/2) =>

50 - 49.85 =>

0.15

0.15% of the babies will be more than 9.4 lbs

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