<prompt> The length of human pregnancies from conception to birth can be approximated a normal distribution with a mean of 265 days and a standard deviation of 15 days. What percentage of all pregnancies will last between 250 and 280 days?38545868  <response>: NormalGaussian curve:Is bilaterally symmetrical, bell-shapedIs bases on mean μ and standard deviation σ Mean, Median and Mode coincide Mean Median ModeHas Mean μ 0 SD σ 1Mean 1SD μ 1σ covers 68 valuesMean 2SD μ 2σ covers 95 valuesMean 3SD μ 3σ covers 99 values- In a Normal distribution, 50 of values lie above the mean and 50 lie below the mean.Mean is 265 days , SD 15Mean 1 SD 250, 280As Mean 1 SD covers 68 values.So percentage of all pregnancies will last between 250 and 280 days is 68. 