a. 10 051.

b. 50 051.

\(90-5\times\left(2\times x-3\right)=45\)

\(=>5\times\left(2\times x-3\right)=90-45\)

\(=>5\times\left(2\times x-3\right)=45\)

\(=>2\times x-3=45:5\)

\(=>2\times x-3=9\)

\(=>2\times x=9+3\)

\(=>2\times x=12\)

\(=>x=12:2\)

\(=>x=6\)

\(#NqHahh\)

\(MSC=18\Rightarrow18:3=6;18:9=2\) 

\(\dfrac{2}{3}=\dfrac{2\times6}{3\times6}=\dfrac{12}{18}\)

\(\dfrac{4}{9}=\dfrac{4\times2}{9\times2}=\dfrac{8}{18}\)

\(\dfrac{7}{18}\) Giữ nguyên phân số

\(#NqHahh\)

\(18\times\left(\dfrac{19191919}{21212121}+\dfrac{88888}{99999}\right)\)

\(=18\times\left(\dfrac{19191919:1010101}{21212121:1010101}+\dfrac{88888:11111}{99999:11111}\right)\)

\(=18\times\left(\dfrac{19}{21}+\dfrac{8}{9}\right)\)

\(=18\times\left(\dfrac{57}{63}+\dfrac{56}{63}\right)\)

\(=18\times\dfrac{113}{63}=\dfrac{226}{7}\)

\(#NqHahh\)

Sửa đề: \(3\times x+2\times x=805\)

\(=>x\times\left(3+2\right)=805\)

\(=>x\times5=805\)

\(=>x=805:5\)

\(=>x=161\)

Vậy x = 161.

\(#NqHahh\)

\(\dfrac{7}{8}:\dfrac{49}{6}=\dfrac{7}{8}\times\dfrac{6}{49}=\dfrac{3}{28}\)

\(\dfrac{7}{8}-\dfrac{7}{16}-\dfrac{11}{32}\)

\(=\dfrac{14}{16}-\dfrac{7}{16}-\dfrac{11}{32}\)

\(=\dfrac{7}{16}-\dfrac{11}{32}\)

\(=\dfrac{14}{32}-\dfrac{11}{32}\)

\(=\dfrac{3}{32}\)

\(#NqHahh\)

1 năm = 12 tháng

Số tháng của 10 năm là:

\(10\times12=120\) ( tháng )

Vậy...

\(#NqHahh\)

Ta có: \(\dfrac{x}{1}=\dfrac{y}{2}=\dfrac{z}{3}\Rightarrow\dfrac{2x}{2}=\dfrac{6y}{12}=\dfrac{2z}{6}\) 

Áp dụng tính chất dãy tỉ sống bằng nhau, ta có:

\(\dfrac{2x}{2}=\dfrac{6y}{12}=\dfrac{2z}{6}=\dfrac{2x+6y+2z}{2+12+6}=\dfrac{60}{20}=3\)

Do đó:

\(\dfrac{x}{1}=3\Rightarrow x=1.3=3\)

\(\dfrac{y}{2}=3\Rightarrow y=2.3=6\)

\(\dfrac{z}{3}=3\Rightarrow z=3.3=9\)

Vậy x = 3; y = 6; z = 9.

\(#NqHahh\)

\(\dfrac{-3}{2}-2x+\dfrac{3}{4}=-2\)

\(=>-\dfrac{3}{2}-2x=\left(-2\right)-\dfrac{3}{4}\)

\(=>\dfrac{-3}{2}-2x=\dfrac{-11}{4}\)

\(=>2x=\dfrac{-3}{2}-\left(\dfrac{-11}{4}\right)=\dfrac{-3}{2}+\dfrac{11}{4}\)

\(=>2x=\dfrac{5}{4}\)

\(=>x=\dfrac{5}{4}:2=\dfrac{5}{4}.\dfrac{1}{2}\)

\(=>x=\dfrac{5}{8}\)

Vậy...

\(#NqHahh\)