(12 1/2)/(2 1/2) = (16 2/3)
12 1/2 * у = 2 1/2 * 16 2/3 свойство пропорции
12 1/2 * у = 5/2 * 50/3
12 1/2 * у = 250/6
у = 250/6 : 12 1/2 = 250/6 : 25/2
у = 250/6 * 2/25
у = 10/3
у = 3 1/3
Проверка: 12 1/2 : 2 1/2 = 16 2/3 : 3 1/3
25/2 * 2/5 = 50/3 * 3/10
25/5 = 50/10
5 = 5
Ответ: у = 3 1/3.