Question

решите пожалуйста!!!

Answer 1

$1)\;\bigg(\dfrac5{21}+\dfrac2{15}\bigg)+\dfrac2{21}=\bigg(\dfrac5{21}+\dfrac2{21}\bigg)+\dfrac2{15}=\dfrac7{21}+\dfrac2{15}=\dfrac13+\dfrac2{15}=\dfrac{5+2}{15}=\dfrac7{15}$

$2)\;\bigg(\dfrac2{35}+\dfrac3{28}\bigg)+\dfrac1{28}=\bigg(\dfrac3{28}+\dfrac1{28}\bigg)+\dfrac2{35}=\dfrac4{28}+\dfrac2{35}=\dfrac17+\dfrac2{35}=\dfrac{5+2}{35}=\dfrac{7}{35}=\dfrac15$