1)100%-15%=85%
2)(20*85):100=17рублей
<span>57 м 389 мм = </span>57000 миллиметр
8 1/2 : m = 3 2/3 * 1 1/11
17/2 : m = 11/3 * 12/1
17/2 : m = 132/3
17/2 : m = 44
m = 17/2 : 44
m = 17/2 * 1/44
<u>m = 17/88</u>
<u>проверка:</u>
8 1/2 : 17/88 = 3 2/3 * 1 1/11
17/2 * 88/17 = 11/3 * 12/11
88/2 = 132/3
44 = 44