\(\dfrac{30}{7}+\dfrac{10}{9}+\dfrac{19}{7}+\dfrac{35}{9}+\dfrac{21}{4}=\left(\dfrac{30}{7}+\dfrac{19}{7}\right)+\left(\dfrac{10}{9}+\dfrac{35}{9}\right)+5,25=7+5+5,25=17,25\)
\(b,=\left(4\dfrac{2}{7}+2\dfrac{5}{7}\right)+\left(\dfrac{10}{9}+\dfrac{35}{9}\right)+\dfrac{21}{4}\\ =\left(\dfrac{30}{7}+\dfrac{19}{7}\right)+\dfrac{45}{9}+\dfrac{21}{4}\\ =\dfrac{49}{7}+5+\dfrac{21}{4}\\ =7+5+\dfrac{21}{4}\\ =12+\dfrac{21}{4}\\ =\dfrac{48+21}{4}=\dfrac{69}{4}\)
`b) 4 2/7 + 10/9 + 2 5/7 + 35/9 + 5 1/4 = ( 4 2/7 + 2 5/7 ) + ( 10/9 + 35/9 ) + 5 1/4 = ( 30/7 + 19/7 ) + 45/9 + 21/4 = 49 /7 + 5 + 21/4 = 7 + 5 + 21/4 = 12 + 21/4 = 48/4 + 21/4 = 69/4`
4 và 5
