The blood platelet counts of a group of women have a bell-shaped distribution with a mean of 256.3 and a standard deviation of 66.8. (All units are 1000 cells/μL.) Using the empirical rule, find each approximate percentage below. a. What is the approximate percentage of women with platelet counts within 3 standard deviations of the mean, or between 55.9 and 456.7? b. What is the approximate percentage of women with platelet counts between 122.7 and 389.9?

a) In the interval  (  55,9  ;   456,7 ) we will find 99,7 % of all values

b) In the interval  (  122,7  ;  389,9 ) we find 95,4 % of all values

Step-by-step explanation:

For a Normal distribution N (μ ; σ ) the Empirical rule establishes that the intervals:

( μ  ±  σ  )          contains 68,3 % of all values

( μ  ±  2σ  )        contains 95,4 % of all values

( μ  ±  3σ  )        contains 99,7 % of all values

If   N ( 256,3 ; 66,8 )

σ  =  66,8        ⇒   3*σ  = 3 * 66,8  = 200,4

Then:     256,3 - 200,4  =  55,9

And        256,3 + 200,4 = 456,7

a) In the interval  (  55,9  ;   456,7 ) we will find 99,7 % of all values

b) 2*σ  = 2 * 66,8  = 133,6

Then  256,3 - 133,6  = 122,7

And    256,3 + 133,6 = 389,90

Then in the interval  (  122,7  ;  389,9 ) we find 95,4 % of all values

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