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

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.