+817 I need help to set up this proportion
In Linguistics $101,$ the ratio of the number of juniors to the number of seniors is $3:2$. When six more juniors join the class, and one senior drops the class, the ratio of the number of juniors to the number of seniors becomes $18:7$. How many students are in the class after these changes?
+129881 Call the number of original Juniors = J Call the number of original Seniors = S
And we know that
J / S = 3 / 2 so that J = (3/2)S (1)
When 6 more Juniors join and one Senior leaves, we have
[ J + 6 ] / [ S -1 ] = 18 / 7 (2)
Sub (1) into (2)
[(3/2)S + 6] / [ S-1] = 18 / 7 cross-multiply
7 [(3/2)S + 6] = 18 [ S - 1] simplify
(21/2)S + 42 = 18S - 18
42 + 18 = 18S - (21/2)S
60 = (36/2)S - (21/2)S
60 = (15/2)S multiply through by 2
120 = 15S
S = 120 / 15 = 8 = number of seniors in original class
J = (3/2)S (3/2) (8) = 12 = number of Juniors in original class
After 6 Juniors join and 1 Senior leaves...we have the ratio (12 + 6) / (8 -1) = 18 / 7
So....there are 25 total students in the class after the changes
