hi friends , im new to salesforce....here is one scenario.... i need to solve it ..i have to create a validation rule on student object.. validation rule should be like this..... can anyone help me....

A student details once entered in Engineering Stream; should not be allowed to be added in Medical/Architecture Stream ; 

Created a Custom Object with a name "Student” with these custom fields.

a. Student Name

b. Student Email Address

c. Student Roll Number (unique number allotted for each student)

d. Student Mailing Address

e. Aggregate Marks Obtained (Percentage field).

f. Rank Obtained.

g. Major (Dropdown with Engineering/Medical/Architecture Stream).

h. Exam Conducted on (Date).

: