Ответ: 12; 5 5/6; 8; 10 1/5; 15 1/2.
Пошаговое объяснение:
4) 1 3/5 * 7 1/2 = (1*5+3)/5 * (7*2+1)/2 = 8/5 * 15/2 = 8*15/5*2 = 120/10 = 12*10/10 = 12
8) 4 1/6 * 1 2/5 = (4*6+1)/6 * (1*5+2)/5 = 25/6 * 7/5 =
= 25*7/6*5 = 175/30 = 35*5/6*5 = 35/6 = (30+5)/6 =
= 30/6 +5/6 = 5 + 5/6 = 5 5/6
12) 7 5/9 * 1 1/17 = (7*9+5)/9 * (1*17+1)/17 =
= 68/9 * 18/17 = 68*18/9*17 = 68*2*9/9*17 = 68*2/17 =
= 136/17 = 8
3) 5 * 2 1/25 = 5/1 * (2*25+1)/25 = 5/1 * 51/25 =
= 5*51/1*25 = 5*51/ 5*5 = 51/5 = (50+1)/5 = 50/5 + 1/5 =
= 10 + 1/5 = 10 1/5
6) 15 * 1 1/30 = 15/1 * (1*30+1)/30 = 15/1 * 31/30 =
= 15*31/1*30 = 15*31 /15*2 = 31/2 = (30+1)/2 =
= 30/2 + 1/2 = 15 + 1/2 = 15 1/2