Propene reacts with $\mathrm{HBr}$ in the absence of peroxide to give mainly

The proton adds to the terminal carbon (Markovnikov rule) to form the more stable secondary carbocation, which is captured by $\mathrm{Br}{}^{-}$. The product is $\mathrm{CH}{}_3-\mathrm{CHBr}-\mathrm{CH}{}_3$.