TÍNH NHANH: 3/4+2/5+1/4+3/5 4/5X3/7+4/5X4/7 2/3X3/4X4/5X5/6 2/5X7/4-2/5X3/7 4/5-2/3+ 1/5-1/3 13/4X2/3X4/13X3/2 Cần gấp

Đáp án + Giải thích các bước giải:

$\dfrac{3}{4}$ + $\dfrac{2}{5}$  + $\dfrac{1}{4}$ + $\dfrac{3}{5}$ = 1 + 1 = 2

$\dfrac{4}{5}$ x  $\dfrac{3}{7}$  + $\dfrac{4}{5}$ x $\dfrac{4}{7}$ = $\dfrac{4}{5}$ ( $\dfrac{3}{7}$ + $\dfrac{4}{7}$ ) = $\dfrac{4}{5}$ . 1 = $\dfrac{4}{5}$
$\dfrac{2}{3}$ x $\dfrac{3}{4}$ x $\dfrac{4}{5}$ x $\dfrac{5}{6}$ = $\dfrac{1}{2}$ x $\dfrac{2}{3}$ = $\dfrac{1}{3}$ 
$\dfrac{2}{5}$ x $\dfrac{7}{4}$ - $\dfrac{2}{5}$ x $\dfrac{3}{7}$ = $\dfrac{7}{10 }$ - $\dfrac{6}{35}$ = $\dfrac{37}{70}$ 
$\dfrac{13}{4}$ x $\dfrac{2}{3}$  x $\dfrac{4}{13}$ x $\dfrac{3}{2}$ = ($\dfrac{13}{4}$ x $\dfrac{4}{13}$ ) x  ($\dfrac{2}{3}$ x $\dfrac{3}{2}$ ) = 1 x 1 = 1