A proportion is a statement that two ratios are equal: a:b = c:d, \({a \over b} = {c \over d}\). To solve proportions with a variable term, cross-multiply: \({a \over 8} = {3 \over 6} \), 6a = 24, a = 4.
In a class of 26 students, 15 are taking German and 15 are taking Spanish. Of the students studying German or Spanish, 10 are taking both courses. How many students are not enrolled in either course?
| 6 | |
| 15 | |
| 21 | |
| 12 |