1.
7/12 + 1/6 = 7/12 + 2/12 = 9/12 = 3/4 = 0,75
1 1/3 * 3/10 = 4/3 * 3/10 = 4/10 = 0,4
4/10 : 4/5 = 4/10 * 5/4 = 1/2 = 0,5
0,75 - 0,5 = 0,25
2.
2/15 * 5/6 = 1/9
1/12 * 1 1/4 = 1/12 * 5/4 = 5/48
5/48 + 1/16 = 5/48 + 3/48 = 8/48 = 1/6
1/6 - 1/9 = 3/18 - 2/18 = 1/18
3.
2 1/2 - 2 = 1/2
1/2 * 3 = 3/2 = 1 1/2 = 1,5
1,5 + 0,5 = 2
2 : 6 = 1/3
4.
1 3/8 - 1/4 = 1 3/8 - 2/8 = 9/8 = 1 1/8
1 1/8 + 5/12 = 1 3/24 + 10/24 = 1 13/24
1 13/24 * 2 = 37/24 * 2 = 37/12 = 3 1/12
3 1/12 : 37 = 37/12 * 1/37 = 1/12
5.
1/2 * 2/3 = 1/3
1/3 + 5/8 = 8/24 + 15/24 = 23/24
5/12 + 13/24 = 10/24 + 13/24 = 23/24
23/24 : 23/24 = 1
х уч=10%
х=800*10:100=80 уч в шесых классах
80=100%
х дев=45%
х=80*45:100=36 девочек в шестых классах
80-36=44 мальчика