Recall and use the equation resistance = p.d. / current, R = V/I

Recall and use the equation for two resistors used as a potential divider R₁/R₂ = V₁/V₂

Recall and use in calculations, the fact that: (a) the current at every point in a series circuit is the same (b) the sum of the currents entering a junction in a parallel circuit is equal to the sum of the currents that leave the junction (c) the total p.d. across the components in a series circuit is equal to the sum of the individual p.d.s across each component (d) the p.d. across an arrangement of parallel resistances is the same as the p.d. across one branch in the arrangement of the parallel resistances