\[\bar{X}\sim N(\mu ,\frac{\sigma ^{2}}{n})
P(\left | \bar{X} - \mu \right | < 15)\]
\[\bar{X}\sim N(\mu ,\frac{\sigma ^{2}}{n})
P(\left | \bar{X} - \mu \right | < 15)\]
\[\bar{X}\sim N(\mu ,\frac{\sigma ^{2}}{n})
P(\left | \bar{X} - \mu \right | < 15)\]
\[P(-15 < \bar{X}- \mu < 15)\]
\[P(-15 < \bar{X}- \mu < 15)\]