20000 = 100\%
20000 : 100 = 200 (1\%)
200*13=2600 (налог)
20000 - 2600 = 17400 (рублей)
5/14 = 15/42, 8/21 = 16/42,
5/14 < 8/21,
31/88 = 310/880, 112/80 = 1232/880,
31/88 < 112/80
1) 8 : 2/9 = 8 * 9/2 = 36 лет отцу
2) 36 : 3/5 = 36 * 5/3 = 60 лет деду