Brian conducts a study to examine the ability of boys and girls in solving difficult mathematical problems. he expects girls to perform much better than boys and communicates his expectation to the participants in a subtle manner. this is an example of

This is an example of Experimenter bias. In research itself stated that girls have more multi tasking skills than boys. Boys can concentrate only on a single thing but girls have the ability to do multiple things at the same time. So even in mathematical problems girls can solve easily and find different solution to the same problem but boys will think in only one way to achieve the solution.