C. Thomas Edison was born

Để điều chế 23g rượu etylic từ tinh bột, hiệu suất thuỷ phân tinh bột và lên men glucozơ tương ứng là 90% và 80%. Khối lượng tinh bột cần dùng là

A. 60g

B. 56,25g

C. 56g

D. 50g

1. x-5=-12 => x=-12+5 => x=-7

Vậy x=-7

2. \(\dfrac{10.7-10}{5-15}=\dfrac{10\left(7-1\right)}{5\left(1-3\right)}=\dfrac{10.6}{-2.5}=\dfrac{2.3}{-1.1}=\dfrac{6}{-1}=-6\)

Câu 1:

A = \(\dfrac{-7}{12}+\dfrac{11}{8}-\dfrac{5}{9}=\dfrac{-42}{72}+\dfrac{99}{72}-\dfrac{40}{72}=\dfrac{-42+99-40}{72}=\dfrac{17}{72}\)

\(B=\dfrac{1}{7}-\dfrac{8}{7}:8-3:\dfrac{3}{4}.2^2=\dfrac{1}{7}-\dfrac{8}{7}.\dfrac{1}{8}-3.\dfrac{4}{3}.4=\dfrac{1}{7}-\dfrac{1}{7}-16=0-16=-16\)

\(C=1,4.\dfrac{15}{49}-\left(\dfrac{4}{5}+\dfrac{2}{3}\right):\dfrac{11}{5}=\dfrac{7}{5}.\dfrac{15}{49}-\dfrac{22}{15}.\dfrac{5}{11}=\dfrac{3}{7}-\dfrac{2}{3}=\dfrac{9-14}{21}=-\dfrac{5}{21}\)

Vậy A=\(\dfrac{17}{72};B=-16;C=\dfrac{-5}{21}\)

Câu 2:

a. \(\dfrac{-11x}{12}+\dfrac{3}{4}=-\dfrac{1}{6}\)

\(\Rightarrow\dfrac{-11x}{12}=-\dfrac{1}{6}-\dfrac{3}{4}\)

\(\Rightarrow\dfrac{-11x}{12}=\dfrac{-2}{12}-\dfrac{9}{12}\)

\(\Rightarrow\dfrac{-11x}{12}=\dfrac{-11}{12}\)

\(\Rightarrow-11x=\dfrac{-11.12}{12}\)

\(\Rightarrow-11x=-11\Rightarrow x=1\)

Vậy x=1

b. \(3-(\dfrac{1}{6}-x).\dfrac{2}{3}=\dfrac{2}{3}\Rightarrow3-\left(\dfrac{1}{6}-x\right)=1\)

\(\Rightarrow-(\dfrac{1}{6}-x)=1-3\Rightarrow\dfrac{1}{6}+x=-2\)

\(\Rightarrow x=2-\dfrac{1}{6}\Rightarrow x=\dfrac{11}{6}\)

Vậy x = \(\dfrac{11}{6}\)

Câu 4:

Ta có: \(\dfrac{1}{2.3}=\dfrac{1}{6}\)

\(\dfrac{1}{2}-\dfrac{1}{3}=\dfrac{3}{6}-\dfrac{2}{6}=\dfrac{1}{6}\)

\(\Rightarrow\dfrac{1}{2.3}=\dfrac{1}{2}-\dfrac{1}{3}\)