ПРОПОРЦИИ
1. X/15 = 4/5
2. 2/x = 6/7
3. 8/9 = x/27
4. 10/23= 4/x

1. x/15 = 4/5;  x = (4*15)/5 = 4*3 = 12;

2. 2/x = 6/7;  x = (2*7)/6 = 7/3 = 2 1/3;

3. 8/9 = x/27;  x = (8*27)/9 = 8*3 = 24;

4. 10/23= 4/x;  x = (4*23)/10 = (2*23)/5 = 46/5 = 9 1/5;