1. Given that (S)-bromobutane has a specific rotation of +30.5 and (R)-bromobutane has a specific rotation of -30.5, what is the optical purity of a mixture whose specific rotation was found to be +10.5?

2. Consider that (S)-bromobutane has a specific rotation of +18.1 and (R)-bromobutane has a specific rotation of -18.1 Which isomer is dominant and what is the optical purity of a mixture, of (R)- and (S)-bromobutane, whose specific rotation was found to be -10.4?