On a certain river a paddle boat travels 8 miles upstream (against the current) in the same amount of time and travel 16 miles downstream (with the current). if the current of the river is 4 mph determine the speed of the boat in still water.

Scores on the cognitive scale of the bayley-scales of infant and toddler development range from 1 to 19, with a standard deviation of 3. calculate the margin of error in estimating the true mean cognitive scale score, with 99% confidence, if there are 12 infants and toddlers in a sample.