The 7-digit numbers in a given area code have the form ABC-, where B, C and X can be any digit 0-7 and A is restricted to 2-8. How many 7-digit numbers are possible in a single area code?

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.