\(\dfrac{1}{5}+\dfrac{5}{9}+\dfrac{4}{5}+\dfrac{1}{9}+\dfrac{3}{9}\)
\(=\left(\dfrac{5}{9}+\dfrac{1}{9}+\dfrac{3}{9}\right)+\left(\dfrac{1}{5}+\dfrac{4}{5}\right)\)
=1+1
=2
Bài 5 :
1/5 + 5/9 + 4/5 + 1/9 + 3/9=(1/5+4/5)+(5/9+1/9+3/9)
=5/5+9/9
=1+1
=2
( 5/9 + 1/5 + 3/9 ) x ( 1/5 + 4/5 )
= 9/9 + 5/5
= 1 + 1
= 2