The alkene shown reacts with $\mathrm{HBr}$ and a peroxide, $\mathrm{ROOR}$. Which structure is the major product?

The alkene is 2-methylbut-2-ene. In the radical chain the bromine atom adds to the less substituted carbon (C-3) so that the more stable tertiary radical forms at C-2; this radical takes H from $\mathrm{HBr}$. The product is 2-bromo-3-methylbutane, the anti-Markovnikov isomer.