Question

Bài 2 Tính nhanh

a) \(\dfrac{5}{23}\) x \(\dfrac{17}{26}\) + \(\dfrac{5}{23}\) x \(\dfrac{10}{26}\) - \(\dfrac{5}{23}\)

b) \(\dfrac{1}{7}\) x \(\dfrac{5}{9}\) + \(\dfrac{5}{9}\) x \(\dfrac{2}{7}\) + \(\dfrac{5}{9}\) x \(\dfrac{1}{7}\) + \(\dfrac{5}{9}\) x \(\dfrac{3}{7}\)

Answer 1

a)\(\dfrac{5}{23}.\dfrac{17}{26}+\dfrac{5}{23}.\dfrac{10}{26}-\dfrac{5}{23}\)

\(=\dfrac{5}{23}\left(\dfrac{17}{26}+\dfrac{10}{26}-1\right)\)

\(=\dfrac{5}{23}.\left(\dfrac{27}{26}-1\right)\)

\(=\dfrac{5}{23}.\dfrac{1}{26}\)

\(=\dfrac{5}{598}\)

b)\(\dfrac{1}{7}.\dfrac{5}{9}+\dfrac{5}{9}.\dfrac{2}{7}+\dfrac{5}{9}.\dfrac{1}{7}+\dfrac{5}{9}.\dfrac{3}{7}\)

\(=\dfrac{5}{9}.\left(\dfrac{1}{7}+\dfrac{2}{7}+\dfrac{1}{7}+\dfrac{3}{7}\right)\)

\(=\dfrac{5}{9}.1=\dfrac{5}{9}\)

Answer 2

a)\(\dfrac{5}{23}.\dfrac{17}{26}+\dfrac{5}{23}.\dfrac{10}{26}-\dfrac{5}{23}\)

\(=\dfrac{5}{23}.\left(\dfrac{17}{26}+\dfrac{10}{26}-1\right)\)

\(=\dfrac{5}{23}.\left(\dfrac{27}{26}-\dfrac{26}{26}\right)\)

=\(\dfrac{5}{23}.\dfrac{1}{26}\)

\(=\dfrac{5}{598}\)

b)\(\dfrac{1}{7}.\dfrac{5}{9}+\dfrac{5}{9}.\dfrac{2}{7}+\dfrac{5}{9}.\dfrac{1}{7}+\dfrac{5}{9}.\dfrac{3}{7}\)

\(=\dfrac{5}{9}.\left(\dfrac{1}{7}+\dfrac{2}{7}+\dfrac{1}{7}+\dfrac{3}{7}\right)\)

\(=\dfrac{5}{9}.\left(\dfrac{7}{7}\right)\)

=\(\dfrac{5}{9}.1\)

\(=\dfrac{5}{9}\)

Answer 3

a)\(=\dfrac{5}{23}\cdot\left(\dfrac{17}{26}+\dfrac{10}{26}-1\right)=\dfrac{5}{23}\cdot\dfrac{1}{26}=\dfrac{5}{598}\)

b)\(=\dfrac{5}{9}\cdot\left(\dfrac{1}{7}+\dfrac{2}{7}+\dfrac{1}{7}+\dfrac{3}{7}\right)=\dfrac{5}{9}\cdot1=\dfrac{5}{9}\)

Hi Hi