\(D=\frac{2}{1.4}+\frac{2}{4.7}+...+\frac{2}{97.100}\)
\(3D=\frac{2.3}{1.4}+\frac{2.3}{4.7}+...+\frac{2.3}{97.100}\)
\(3D=2\left(\frac{3}{1.4}+\frac{3}{4.7}+...+\frac{3}{97.100}\right)\)
\(3D=2\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{100}\right)\)
\(3D=2\left(1-\frac{1}{100}\right)\)
\(3D=2\cdot\frac{99}{100}\)
\(3D=\frac{99}{50}\)
\(D=\frac{99}{50}:3\)
\(D=\frac{33}{50}\)
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