Question

Tính hợp lí 

a) ( 4\(\dfrac{2}{5}\) + 2\(\dfrac{3}{7}\) ) - ( 2\(\dfrac{2}{5}\) - 5\(\dfrac{4}{7}\) ) 

b) ( 10\(\dfrac{3}{8}\) - 3\(\dfrac{4}{5}\) ) + ( 4\(\dfrac{5}{8}\) - 1\(\dfrac{1}{5}\) ) 

Answer 1

a) \(\left(4\dfrac{2}{5}+2\dfrac{3}{7}\right)-\left(2\dfrac{2}{5}-5\dfrac{4}{7}\right)\)

\(=\left(\dfrac{22}{5}+\dfrac{17}{7}\right)-\left(\dfrac{12}{5}-\dfrac{39}{7}\right)\)

\(=\left(\dfrac{22}{5}-\dfrac{12}{5}\right)+\left(\dfrac{17}{7}+\dfrac{39}{7}\right)\)

\(=2+8=10\)

\(b,\left(10\dfrac{3}{8}-3\dfrac{4}{5}\right)+\left(4\dfrac{5}{8}-1\dfrac{1}{5}\right)\)

\(=\left(\dfrac{83}{8}-\dfrac{19}{5}\right)+\left(\dfrac{37}{8}-\dfrac{6}{5}\right)\)

\(=\left(\dfrac{83}{8}+\dfrac{37}{8}\right)-\left(\dfrac{19}{5}+\dfrac{6}{5}\right)\)

\(=15-5=10\)