\(\Rightarrow A=\frac{4}{3.7}+\frac{4}{7.11}+\frac{4}{11.15}+...+\frac{4}{95.99}\)

\(A=4\left(\frac{1}{3.7}+\frac{1}{7.11}+\frac{1}{11.15}+...+\frac{1}{95.99}\right)\)

\(A=4.\frac{1}{4}\left(\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{15}+...+\frac{1}{95}-\frac{1}{99}\right)\)

\(A=\frac{4}{4}\left(\frac{1}{3}-\frac{1}{99}\right)\)

\(A=\frac{32}{99}\)

\(\frac{4}{3}.\frac{4}{7}+\frac{4}{7}.\frac{4}{11}+\frac{4}{11}.\frac{4}{15}+...+\frac{4}{95}.\frac{4}{99}\)

\(\Leftrightarrow\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{15}+...+\frac{1}{95}-\frac{1}{99}\)

\(=\frac{1}{3}-\frac{1}{99}=\frac{32}{99}\)

\(\Leftrightarrow A=\frac{32}{99}\)

sai rồi

\(\frac{2,4\times1994\times2+1,6\times3996\times3+1,2\times4010\times4}{3+7+11+...+95+99-275}\)

\(=\frac{0,2\times6\times2\times2\times997\times2+0,2\times8\times6\times666\times3+0,2\times6\times2\times2005\times4}{\left(99+3\right)\times49:2-275}\)

\(=\frac{0,2\times6\times8\times997+0,2\times8\times6\times666\times3+0,2\times6\times8\times2005}{2499-275}\)

\(=\frac{0,2\times6\times8\times\left(997+666\times3+2005\right)}{2224}\)

\(=\frac{0,2\times2\times3\times8\times\left(997+1998+2005\right)}{8\times2\times0,2\times695}\)

\(=\frac{3\times\left(2995+2005\right)}{695}\)

\(=\frac{3\times5000}{695}=\frac{3\times1000\times5}{5\times139}\)

\(=\frac{3\times1000}{139}=\frac{3000}{139}\)

=???????????

tinh nhanh 2 bai nay giup mk di ma cac ban oi

tìm x 275% : x - 3/4 : x + 1,2  : x = 1,6                                                       giúp mik với, ai làm đg mik tick ng đó!!!