2 1/2 : 3 1/2 = n : 2
(2 1/2) / (3 1/2) x 2=1 3/7, so that:
2 1/2 : 3/12 = 1 3/7 : 2
2+ 1/2 : 3 + 1/2 = n : 2
2 + 1/2 = 5/2
3+ 1/2 = 7/2
So
(5/2) / (7/2) = n / 2
5 / 7 = n / 2 cross-multiply
10 = 7n divide both sides by 7
10 / 7 = n
