A scientist is studying a rare breed of guinea pigs It is as

A scientist is studying a rare breed of guinea pigs. It is assumed that their weights have a normal distribution. A preliminary study of 23 of them gives their weights a standard deviation of 142 grams. How many more will she need to study to get a 95% confidence interval with an error of not more than 28 ounces?

Solution

Standard error = (z*SD)/sqrt(n)

z for 95% CI = 1.96

Therefore,

28 = (1.96 * 142) / sqrt(n)

=> sqrt(n) = (1.96 * 142)/28 = 9.94

=> n = 98.80 ~ 99

Therefore , (99-23) = 76 more pigd to study