Describe difference between direct variation and joint variation

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.

The graph of a curve that passes the vertical line test is a:

Gabrielle's age is three times mikhail's age. the sum of their ages is 40 . what is mikhail's age? __ years old