21 номер даю 20 балов
Урок через 3минуты быстрее плииииз

a).  1/4 * 5/8 = 5/32

б). 7/15 * 5/49 = 1/15 * 5/7 = 1/3 * 1/7 = 1/21

в). 16/9 * 3/10 = 16/3 * 1/10 = 8/3 * 1/5 = 8/15

г). 10/13 * 26/45 = 10 * 2/45 = 20/45 = 4/9

д). 6/9 * 27/3 = 6/9 * 9 = 6  

e). 7/15 * 5/14 = 7/3 * 1/14 = 1/3 * 1/2 = 1/6

ж). 3/32 * 8/27 = 3/4 * 1/27 = 1/4 * 1/9 = 1/36

з). 51/64 * 12/17 = 3/64 * 12 = 36/64 = 9/16