а) 15:10=x:40; г) х:1 1/3=6:4; б) 3,6:4,2=6:х; д) х:3,86=2,5:2 1/2. в) 3:х=3/8:1/4;

№115 : 10 = х;х = 15 : 10;х = 15/10;х = 1 5/10;х = 1 1/2.Проверка:15 : 10 = 1 1/2;15/10 = 1 1/2;1 1/2 = 1 1/2.№2х : 1 1/3 = 6 : 4;х : 4/3 = 6/4;х * 3/4 = 6/4;х * 3/4 * 4/3 = 6/4 * 4/3;х = 24/12;х = 2.Проверка:2 : 1 1/3 = 6 : 4;2 : 4/3 = 6/4;2 * 3/4 = 6/4;6/4 = 6/4.№33,6 : 4,2 = 6 : х;3 6/10 : 4 2/10 = 6 : х;36/10 : 42/10 = 6 : х;36/10 * 10/42 = 6 : х;36/42 = 6 : х;6/7 = 6 : х;х = 6 : 6/7;х = 6 * 7/6;х = 7.Проверка:3,6 : 4,2 = 6 : 7;36/10 : 42/10 = 6/7;36/10 * 10/42 = 6/7;36/42 = 6/7;6/7 = 6/7.№4х : 3,86 = 2,5 : 2 1/2;х : 3 86/100 = 2 5/10 : 2 1/2;х : 386/100 = 25/10 : 5/2;х : 386/100 = 25/10 * 2/5;х : 386/100 = 50/50;х : 386/100 = 1;х * 100/386 = 1;х * 100/386 * 386/100 = 1 * 386/100;х = 386/100 = 3 86/100 = 3 43/50.Проверка:386/100 : 386/100 = 2,5 : 2 1/2;386/100 * 100/386 = 25/10 * 2/5;1 = 1.№53 : х = 3/8 : 1/4;3 : х = 3/8 * 4/1;3 : х = 12/8;х = 3 : 12/8;х = 3 * 8/12;х = 2.Проверка:3 : 2 = 3/8 : 1/4;3/2 = 12/8;3/2 = 3/2.