\(A=\dfrac{7}{19}\cdot\dfrac{8}{11}+\dfrac{7}{19}\cdot\dfrac{3}{11}+\dfrac{12}{19}\\ A=\dfrac{7}{19}\left(\dfrac{8}{11}+\dfrac{3}{11}\right)+\dfrac{12}{19}\\ A=\dfrac{7}{19}\cdot1+\dfrac{12}{19}\\ A=\dfrac{19}{19}=1\)
A = 7/19.8/11+7/19.3/11+12/19
A = 7/19. . (8/11 + 3/11) + 12/19
A = 7/19 . 1 + 12/19
A = 7/19 + 12/19
A = 1
Ta có: \(A=\dfrac{7}{19}\cdot\dfrac{8}{11}+\dfrac{7}{19}\cdot\dfrac{3}{11}+\dfrac{12}{19}\)
\(=\dfrac{7}{19}\cdot\left(\dfrac{8}{11}+\dfrac{3}{11}\right)+\dfrac{12}{19}\)
\(=\dfrac{7}{19}+\dfrac{12}{19}=1\)
