In about percent of families, the relationship between an adolescent and his/her parents is marked by serious conflict and behavioral problems. these issues often predate adolescence and, as children, there may have been problematic relationships with peers.

I believe the answer is 25%
The conflict and behavioral problems that arise are most likely caused by misunderstanding between the parents and the children.
The parents failed to understand that the change and behavior that happen to adolescents might be necessary for them to fit in and the children failed to understand that some of the changes might cause negative things for them in the long run.