(2целых 4/7-2,5):(1/6:1/21)

(18/7-25/10):(1/6:1/21)=(180/70-175/70):(1/6×21/1)=5/70:7/2=10/490=1/49

(2 4/7 - 2,5) : (1/6 : 1/21) = 1/49, 1) 2 4/7 - 2,5 = 18/7 - 5/2 = 36/14 - 35/14 = 1/14, 2) 1/6 : 1/21 = 1/6 * 21/1 = 7/2 = 3 1/2, 3) 1/14 : 3 1/2 = 1/14 : 7/2 = 1/14 * 2/7 = 1/49