\(75\%\times y+\dfrac{3}{4}\times y-y=30\)
\(\dfrac{3}{4}\times y+\dfrac{3}{4}\times y-1\times y=30\)
\(\left(\dfrac{3}{4}+\dfrac{3}{4}-1\right)\times y=30\)
\(\dfrac{1}{2}\times y=30\)
\(y=30:\dfrac{1}{2}\)
\(y=60\)

\(S_{ABCD}=AB\cdot BC=3a\cdot6a=18a^2\)

\(20\left(x-2\right)+6\left(x-5\right)-16x=100\)
\(\Rightarrow20x-40+6x-30-16x=100\)
\(\Rightarrow\left(20x+6x-16x\right)-\left(40+30\right)=100\)
\(\Rightarrow10x-70=100\)
\(\Rightarrow10x=170\)
\(\Rightarrow x=17\)

\(102:x=6,8\)
\(x=102:6,8\)
\(x=15\)
\(-------\)
\(x\times2,5=31,25\)
\(x=31,25:2,5\)
\(x=12,5\)

Đề nghị bạn nếu copy thì phải ghi "Tham khảo"!

a/Lãi suất tiết kiệm:
\(6030000:6000000-100\%=0,005=0,5\%\)
b/Số tiền gốc và lãi rút ra được tất cả trong 2 tháng:
\(6030000+6030000\cdot0,5\%=6060150\left(đ\right)\)

\(\dfrac{3}{13}\cdot\dfrac{6}{11}+\dfrac{3}{13}-\dfrac{9}{11}\cdot\dfrac{9}{11}-\dfrac{3}{13}\cdot\dfrac{4}{11}\)
\(=\dfrac{3}{13}\left(\dfrac{6}{11}+1-\dfrac{4}{11}\right)-\dfrac{81}{121}\)
\(=\dfrac{3}{13}\cdot\dfrac{13}{11}-\dfrac{81}{121}\)
\(=\dfrac{3}{11}-\dfrac{81}{121}=-\dfrac{48}{121}\)

a/\(\dfrac{5}{7}=\dfrac{5}{7}\)
\(3=\dfrac{3\times7}{7}=\dfrac{21}{7}\)
b/\(8=\dfrac{8\times25}{25}=\dfrac{200}{25}\)
\(\dfrac{6}{5}=\dfrac{6\times5}{5\times5}=\dfrac{30}{25}\)