28/49 =4/7
9(4/5) - 4(13/20) = 9(16/20) - 4(13/20) = 5(3/20)
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1)4*3=12км-прошёл пешеход за 3 часа.
2)10-4=6км/ч-скорость сближения.
3)12:6=через 2 часа.
-9 -5 -1 3 7 11 15 19 23 27 31 35 39 43 47 51 55 59 67 71 75 79 83 85 89 93