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20/7 x [(1/6 + 2/3) : (2 - 4/3)] =

= 20/7 x [(1/6 + 4/6) : ( 6/3 - 4/3)] =

= 20/7 x [(5/6) : (2/3)] =

= 20/7 x [(5/6) x 3/2)] =

= 20/7 x [(5 x 3)/(6 x 2)] =

= 20/7 x [5/4] = 

=  20 x 5 / (7 x 4) =

= 5 x 5 / 7 = 25/7.

Ciao @nadya

Moltiplica per 20/7 il quoziente tra la somma di 1/6 e 2/3 e la differenza di 2 e 4/3.

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$\small \dfrac{20}{7}·\dfrac{\dfrac{1}{6}+\dfrac{2}{3}}{2-\dfrac{4}{3}}=$

$\small =\dfrac{20}{7}·\dfrac{\dfrac{1+4}{6}}{\dfrac{6-4}{3}}=$

$\small =\dfrac{20}{7}·\dfrac{\dfrac{5}{6}}{\dfrac{2}{3}}=$

$\small =\dfrac{20}{7}·\dfrac{5}{6}·\dfrac{3}{2}=$

$\small =\dfrac{\cancel{20}^{10}}{7}·\dfrac{5}{6}·\dfrac{3}{\cancel2_1}=$

$\small =\dfrac{10}{7}·\dfrac{5}{\cancel6_2}·\dfrac{\cancel3^1}{1}=$

$\small =\dfrac{10}{7}·\dfrac{5}{2}·\dfrac{1}{1}=$

$\small =\dfrac{\cancel{50}^{25}}{\cancel{14}_7}= \dfrac{25}{7}$