A Student Measured the Optical Activity of an Unknown Sugar

Multiple Choice

A student measured the optical activity of an unknown sugar at two different concentrations. The results of his measurements are shown below. Given that the sample cell had a path length of 10.0 cm, calculate the specific rotation for the unknown sugar. (Hint: Consider each measurement of plane polarized light has a true reading and a "ghost" reading 180° from the true reading) .
Concentration observed rotation
2) 00 g sugar in 10.0 mL water +159.1°
5) 00 g sugar in 10.0 mL water +127.8°

A) -10.5°
B) +25.6°
C) +79.5°
D) -105°
E) +256°