Based on Markonikov's rule, H-X hydrogen will be added onto the carbon (double bond) with more hydrogens. Therefore, the LHS and the middle makes sense. But why is the RHS product possible ? Hydrogen is adding onto a carbon which is not a double bond
The reason that that RHS product is possible is because a hydride shift can take place. As a result, the positive charge is in a more stable position (tertiary). To summarize, the electrons from the pi bond will attack HBr and will form a carbocation. A hydride shift will occur which places the positive charge at the methyl group. Then the bromide ion will attack which yields the product on the RHS.
