Question

Tính nhanh a) 25/4*9 + 25/9*14 + 25/14*19 +...+ 25/2004*2009

b) 20,07:0,2+20,07*91+20,07:0,25

c) 50,08*34 - 536,46 + 50,08 * 66 - 436,54

Answer 1

\(\text{Ta có : }\)\(\frac{25}{4.9}+\frac{25}{9.14}+\frac{25}{14.19}+......+\frac{25}{2004.2009}\)

\(=5.\left(\frac{5}{4.9}+\frac{5}{9.14}+\frac{5}{14.19}+......+\frac{5}{2004.2009}\right)\)

\(=5\left(\frac{1}{4}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+......+\frac{1}{2004}-\frac{1}{2009}\right)\)

\(=5\left(\frac{1}{4}-\frac{1}{2009}\right)\)

\(=5.\frac{2005}{8036}=\frac{10025}{8036}\)