Số chẵn bé nhất có 4 chữ số: 1000

Số lẻ lớn nhất có 3 chữ số: 999

Hiệu: 1000 - 999 = 1

\(\dfrac{5}{2.4}+\dfrac{5}{4.6}+...+\dfrac{5}{132.134}\)

\(=2,5\left(\dfrac{2}{2.4}+\dfrac{2}{4.6}+...+\dfrac{2}{132.134}\right)\)

\(=2,5\left(\dfrac{4-2}{2.4}+\dfrac{6-4}{4.6}+...+\dfrac{134-132}{132.134}\right)\)

\(=2,5\left(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{8}+...-\dfrac{1}{134}\right)\)

\(=2,5\left(\dfrac{1}{2}-\dfrac{1}{134}\right)\)

\(=2,5.\dfrac{33}{67}\)

\(=\dfrac{165}{134}\)