In triangle ABC, side BC is extended beyond C to a point D. $\angle ACD = 115^\circ$, and $\angle A : \angle B = 3 : 2$. What is $\angle A$?

Explanation

1. 01

   The exterior angle equals the sum of the two opposite interior angles: $\angle A + \angle B = 115^\circ$.

2. 02

   Split 115° in the ratio $3 : 2$: one part = $115^\circ \div 5 = 23^\circ$.

3. 03

   $\angle A = 3 \times 23^\circ = 69^\circ$.