This formation of a major product and minor product only occurs if the double bond is unsymmetrical (when the carbon atoms involved in the double bond are bonded to different groups), for example in butene. When electrophilic addition takes place with a hydrogen halide (HBr) we will form these two different products. We can see that the hydrogen atom and bromine atom have been added to different sides. If we look at the mechanism we can see which one is going to be the major product by looking at which intermediate has the most stabilised carbocation. Remember that a tertiary carbocation is more stabilised than a secondary carbocation and a secondary carbocation is more stabilised than a primary carbocation. I would then ask the student an exam type question, in order for them to apply this.