Buổi sáng bán được số lít dầu là:
`420 xx 2/5 = 168`(lít)
Cửa hàng còn lại số lít dầu là:

`420-168=252`(lít)

Đáp số: 252 lít

giả coin đây .-.

\(a,1\dfrac{2}{3}+x=\dfrac{-11}{3}\\ \Rightarrow\dfrac{5}{3}+x=\dfrac{-11}{3}\\ \Rightarrow x=\dfrac{-11}{3}-\dfrac{5}{3}\\ \Rightarrow x=\dfrac{-16}{3}\\ b,\dfrac{2}{3}+\dfrac{1}{3}:x=\dfrac{3}{4}\\ \Rightarrow\dfrac{1}{3}:x=\dfrac{3}{4}-\dfrac{2}{3}\\ \Rightarrow\dfrac{1}{3}:x=\dfrac{1}{12}\\ \Rightarrow x=\dfrac{1}{3}:\dfrac{1}{12}\\ \Rightarrow x=4\)

Đáy bé thửa ruộng là:
`80 xx 3/4 =60`(m)

Chiều cao thửa ruộng là:

`60-12=48`(m)

Diện tích thửa ruộng là:

`(80+60)xx48:2=3360`(m²)

Số kg thóc thu được là:
`3360:100xx56,5=1898,4`(kg)

Đáp số: 1898,4kg

\(a,\dfrac{29}{19}+\dfrac{-7}{15}+\dfrac{-8}{15}-\dfrac{10}{19}=\left(\dfrac{29}{19}-\dfrac{10}{19}\right)+\left(\dfrac{-7}{15}+\dfrac{-8}{15}\right)=\dfrac{19}{19}+\dfrac{-15}{15}=1+\left(-1\right)=0\\ b,\dfrac{-7}{9}.\dfrac{6}{13}+\dfrac{-7}{9}.\dfrac{7}{13}+\dfrac{7}{9}=\dfrac{-7}{9}\left(\dfrac{6}{13}+\dfrac{7}{13}\right)+\dfrac{7}{9}=\dfrac{-7}{9}.\dfrac{13}{13}+\dfrac{7}{9}=\dfrac{-7}{9}.1+\dfrac{7}{9}=\dfrac{-7}{9}+\dfrac{7}{9}=0\)

\(c,\dfrac{-3}{7}+\dfrac{15}{26}-\left(\dfrac{2}{13}-\dfrac{3}{7}\right)=\dfrac{-3}{7}+\dfrac{15}{26}-\dfrac{4}{26}+\dfrac{3}{7}=\left(\dfrac{-3}{7}+\dfrac{3}{7}\right)+\left(\dfrac{15}{26}-\dfrac{4}{26}\right)=\dfrac{0}{7}+\dfrac{11}{26}=0+\dfrac{11}{26}=\dfrac{11}{26}\\ d,2.\dfrac{3}{7}+\left(\dfrac{2}{9}-1\dfrac{3}{7}\right)-\dfrac{5}{3}:\dfrac{1}{9}=\dfrac{6}{7}+\dfrac{2}{9}-\dfrac{10}{7}-15=-\dfrac{967}{63}\)

\(\dfrac{a+2b-ab-2b^2}{1-b}=\dfrac{\left(a+2b\right)-b\left(a+2b\right)}{1-b}=\dfrac{\left(1-b\right)\left(a+2b\right)}{1-b}=a+2b\)

ĐKXĐ:\(x\ne\pm2\)

\(\dfrac{5}{x+2}-\dfrac{x-1}{2-x}=\dfrac{12}{x^2-4}+1\\ \Leftrightarrow\dfrac{5\left(x-2\right)}{\left(x-2\right)\left(x+2\right)}+\dfrac{\left(x-1\right)\left(x+2\right)}{\left(x-2\right)\left(x+2\right)}-\dfrac{12}{\left(x-2\right)\left(x+2\right)}-\dfrac{\left(x-2\right)\left(x+2\right)}{\left(x-2\right)\left(x+2\right)}=0\\ \Leftrightarrow\dfrac{5x-10+x^2+x-2-12-x^2+4}{\left(x-2\right)\left(x+2\right)}=0\\ \Rightarrow6x-20=0\\ \Leftrightarrow x=\dfrac{10}{3}\left(tm\right)\)

Độ dài hình tam giác là:
`48xx8:2=192`(dm)

Đáp số: 192dm

Đã có đâu