Tính: 12 giờ 47 phút + 7 giờ 35 phút 

  a, 12 giờ 47 phút + 7 giờ 35 phút             b, 16 ngày 6 giờ - 7 ngày 12 giờ

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 c, ( 12 phút 30 giây + 5 phút 15 giây) x 3    d, 14 giờ 44 phút : 4

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