Statistics help help

Add 1/7 + -1/7 your answer should be reduced to its smallest form and should not be an improper fraction

Write the converse of the following statement: if the trees have no leaves, then it is fall. if the trees have no leaves, then it is fall. the trees have no leaves, therefore it is fall. it is fall since the trees have no leaves. if it is fall, then the trees have no leaves.

What situation is an example of an observational study