4. Выполните умножение: а) 3/7 * 2/5; б) 7/13 * 39/56; в) 3 1/9 * 2 1/7; г) 2 1/7 * 2 4/5; д) 1 1/9 * 3/10; е) 4/11 * 7/12.

Решим примеры на умножение дробей.

a) 3/7 * 2/5 = (3 * 2)/(7 * 5) = 6/35

б) 7/13 * 39/56 = (7 * 39)/(13 * 56) = (7 * 3 * 13)/(13 * 7 * 8) = 3/8

в) 3 1/9 * 2 1/7 = (3 * 9 + 1)/9 * (2 * 7 + 1)/7 = 28/9 * 15/7 = (28 * 15)/(9 * 7) = (4 * 7 * 3 * 5)/(3 * 3 * 7) = (4 * 5)/3 = 20/3 = 6 2/3

г) 2 1/7 * 2 4/5 = (2 * 7 + 1)/7 * (2 * 5 + 4)/5 = 15/7 * 14/5 = (15 * 14)/(7 * 5) = (3 * 5 * 2 * 7)/(7 * 5) = 3 * 2 = 6

д) 1 1/9 * 3/10 = (1 * 9 + 1)/9 * 3/10 = 10/9 * 3/10 = (10 * 3)/(9 * 10) = (3 * 10)/(9 * 10) = 3/9 = 1/3

е) 4/11 * 7/12 = (4 * 7)/(11 * 12) = (4 * 7)/(11 * 4 * 3) = 7/(11 * 3) = 7/33

Ответ:

1. а) 6/35
2. б) 3/8
3. в) 6 2/3
4. г) 6
5. д) 1/3
6. е) 7/33