ABCD is a square and ΔMAB is an equilateral triangle. MC and MD are joined. What is the degree measure of ∠MDC?

Answer: Option D

∠A = ∠B = ∠D = ∠C = 90°
ΔAMB is equilateral
Hence ∠A = 60°
∠DAM = 90° + 60° = 150°
∠ADM $$=\frac{{180}^{\circ }-{150}^{\circ }}{2}=\frac{{30}^{\circ }}{2}=15^{\circ }$$
∠MDC = 90° - 15° = 75°