Enantiomeric excess | Stereoisomers

What is the enantiomeric composition of a mixture that has a specific rotation of + 75° and has an enantiomeric excess of 60%?

Let's say, we have x % of (+) isomer and y % of (-) isomer ⇒ x + y = 100

ee = # moles of 1 enantio. - # moles of the other enantio.# moles of both enantiomers × 100 = x - y100 × 100 ⇒ x - y = 60
 

x + y = 100, x - y = 60 ⇒ 2x = 160 ⇒ x = 80, y = 20.

80% of (+) isomer, 20% of (-) isomer.