6 целых 2/3 см = (6*3+2)/3см =20/3 см .
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20/3 : 2/5*3/10=20/3*5/2*3/10 =100/6*3/10 =(100*3)/(6*10) =5 (см)
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6 целых 2/3 = (6*3+2)/3 =20/3 .