The length of pregnancies are normally distributed with a mean of 268 days and a

Question

The length of pregnancies are normally distributed with a mean of 268 days and a standard deviation of 15 days 17 Ifwe stipulate that a baby is premature if born at least three weeks early, what fraction of babies are born prematurely? 0.0808 0.0668 0.0571 0.0485 Few years ago, in a letter to "Dear Abby" a wife claimed to have given birth 300 days after a brief visit from her husband, who was serving in the Navy. What is the probability that her husband was the actual father of the baby, that is, the probability ofa pregnancy lasting 300 days or longer? 18 0.0228 0.0166 0.0099 0.0068 What middle interval (of days) includes 0.95 fraction of all pregnancies? Round the days to the nearest integer. 19 252 249 243 239 285 287 293 297 Weight of newborn babies in the United States is normally distributed, with a standard deviation of500 grams. The fraction of newborn babies who weight less than 2500 grams is 0.0359. What fraction weight more than 4000 grams? 20 0.1379 0.1230 0.1151 0.1056

Explanation / Answer

17)

option A)

18)

option b

19)

for 95% CI ; z =1.96

hence middle 95% value =mean -/+ z*std deviation =239 to 297

option d

20)

for 0.0359 probability ; zscore =-1.8

therefore mean =2500+1.8*500=3400

hence P(X>4000)=P(Z>(4000-3400)/500)=P(Z>1.2)=0.1151

option C

for normal distribution z score =(X-)/ here mean=       = 268.000 std deviation   == 15.000

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