Question

các bạn giải luôn câu này hộ mk nah! CÁM ƠN!!!!!!!!

\(\frac{3x}{2.5}\) cộng \(\frac{3x}{5.8}\) cộng \(\frac{3x}{8.11}\) cộng \(\frac{3x}{11.14}\)=\(\frac{1}{21}\)

và câu này nữa nha :
\(\frac{3}{4}\) quả dưa nặng \(3\frac{1}{2}\)kg .Hỏi quả dưa nặng bao nhiêu kg ?

MAI MK PHẢI NỘP RỒI !HELP ME !THANK YOU!!!!!!

Answer 1

a, \(3x\left(\frac{1}{2.5}+\frac{1}{5.8}+\frac{1}{8.11}+\frac{1}{11.14}\right)=\frac{1}{21}\)

\(3x.\frac{1}{3}\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-...+\frac{1}{11}-\frac{1}{14}\right)=\frac{1}{21}\)

\(x.\left(\frac{1}{2}-\frac{1}{14}\right)=\frac{1}{21}\)

\(\frac{3x}{7}=\frac{1}{21}\Rightarrow x=\frac{1}{9}\)

Answer 2

\(a,\frac{3x}{2.5}+\frac{3x}{5.8}+\frac{3x}{8.11}+\frac{3x}{11.14}=\frac{1}{21}\)

\(\Leftrightarrow3x\left(\frac{1}{2.5}+\frac{1}{5.8}+\frac{1}{8.11}+\frac{3x}{11.14}\right)=\frac{1}{21}\)

\(\Leftrightarrow3x.\frac{1}{3}\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}\right)=\frac{1}{21}\)

\(\Leftrightarrow x\left(\frac{1}{2}-\frac{1}{14}\right)=\frac{1}{21}\)

\(\Leftrightarrow x.\frac{3}{7}=\frac{1}{21}\)

\(\Leftrightarrow\frac{3x}{7}=\frac{1}{21}\)

\(\Leftrightarrow63x=7\Leftrightarrow x=\frac{1}{9}\)

\(\Leftrightarrow21.9x=7\)

\(\Leftrightarrow189x=7\)

\(\Leftrightarrow x=\frac{1}{27}\)

b, Gọi số ki-lo-gam dưa là a kg(a>0)

Theo bài ra ta có:

\(\frac{3}{4}a=3\frac{1}{2}\Leftrightarrow\frac{3}{4}a=\frac{7}{2}\Leftrightarrow a=\frac{11}{4}\left(kg\right)\)

Vậy số ki-lo-gam dưa là \(\frac{11}{4}\) kg