statistics help please

Assume the duration of human pregnancies can be described by a normal model with mean 285 days and a standard divination of 16 days. At least how many days should the longest 25% of all pregnancies last?

Question

statistics help please

Assume the duration of human pregnancies can be described by a normal model with mean 285 days and a standard divination of 16 days. At least how many days should the longest 25% of all pregnancies last?

anonymous · Answer

diviation* typo

amistre64 · Answer

if we had a zscore, we could look up in a table to find a field value of .2500

anonymous · Answer

My teacher has one online

amistre64 · Answer

what method of calculations do you have to solve this?  ti83, or table?

anonymous · Answer

i have both, z score prefered

anonymous · Answer

by z score you mean the z table thing right?

amistre64 · Answer

yes :)  can you post the table?

anonymous · Answer

attachment

amistre64 · Answer

once we know a suitable value for "z", the formula:$$z=\frac{x-\bar x}{sd}$$can be solved for "x"$$z(sd)+\bar x=x$$

amistre64 · Answer

.2514 is the closest i see to .2500

amistre64 · Answer

can you tell me the zscore of .2514?

amistre64 · Answer

im wondering tho

25% of all pregnancies; maybe we should split that up in 12.5% in each tail

anonymous · Answer

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