Дроби к наименьшему общему знаменателю. 7/8 и 1/12; 4/13 и 3/4; 1/20 и 1/30; 4/15 и 3/10; 1/9 и 1/7; 1/9,1/4 и 1/6; 10/17 и 13/34; 9/14 и 10/21; 3/28,9/14 и 7/8

7/8=21/24, 1/12=2/24;
4/13=16/52, 3/4=39/52;
1/20=3/60, 1/30=2/60;
4/15=8/30, 3/10=9/30;
1/9=7/63, 1/7=9/63;
1/9=4/36, 1/4=9/36, 1/6=6/36;
10/17=20/34, 13/34=13/34;
9/14=27/42, 10/21=20/42;
3/28=6/56, 36/56, 49/56.