Tính bằng cách thuận tiện nhất :
b,21/17 x 13/14 x 56 x 3/42 =
ai nhanh cho 2 tick cần gấp ,.................................................................................................
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21/17 x 13/14 x 56 x 3/42
= 21/17 x 3/42 x 13/14 x 56
= (21 x 3)/(17 x 42) x (13 x 56)/14
= (3/(17 x 2)) x 13 x 4
= 3/34 x 13/4
= 39/136
k mk nha !