if we don't want to get confused what we can do is 2 equations, one that represents the relationship between the box and the candy, and another that represents the money
x = candy
y = box
x = y + 19
x + y = 20
we replace in the second equation the value of x by (y + 19)
x + y = 20
(y + 19) + y = 20
y +y = 20 - 19
2y = 1
y = 1/2
y = 0.5
we replace in the first equation the value of y by its value
x = y + 19
x = 0.5 + 19
x = 19.5
so the candy value is $ 19.5 and the box value is $ 0.5
The sample proportion of the the students that took fewer than the mean number of electives is given by the number of people who took less that the mean number of electives (i.e. 7.63) divided by the total number of students in the sample (i.e. 19). The total number of people who took less than 7.63 electives is 10. Therefore, the required sample proportion is 10 / 19.
