Question

 

4/1.2 + 4/ 2.3+ 4/ 3.4+..... +4/ 99 nhân 100

Answer 1

4/1.2 + 4/2.3 +4/3.4+...+4/99.100

=> 4/1 - 4/2 + 4/2 - 4/3 + 4/3 - 4/4+...+ 4/99 - 4/100

=>4 - 4/100

Answer 2

\(\frac{4}{1.2}+\frac{2}{2.3}+\frac{4}{3.4}+...+\frac{4}{99.100}\)

\(=4.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}\right)\)

\(=4.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{99}-\frac{1}{100}\right)\)

\(=4.\left(1-\frac{1}{100}\right)\)

\(=4.\frac{99}{100}=\frac{99}{25}\)