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the length length of a species of plants is normally distributed with expected value 60 cm. it is known from past experience that seventy five percent of theses flowers have length between 50 and 70 cm. what can we say about the standard deviation of the length of this plant?



Answer :

varshamittal029

The standard deviation of the length of this plant be 25.

m = 60(mean)

Let the standard deviation be s,

As, the probability for 50<x<70 be 0.75

Z = (x−m)/s

for x=50,

Z=0

for x=70,

Z=(70−50)/s=20/s

Now, the probability for 50<x<70 be,

P(50<x<70) = 0.75

In the standard form 0<z<(20/s)

using Z-table, the area from 0 to 20/s,

= 0.75

s = 25

Hence, the standard deviation of the length of this plant be 25.

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