Question

cho A=0,01+0,02+0,03+.............+0,98+0,99 ( tính nhanh 2×A)

 

Answer 1

A = 0.01 + 0.02 + 0.03 +... + 0.98 + 0.99

=> 100A = 1+2+3+...+98+99

=>100A = \(\frac{100.99}{2}\)=4950

=> 2A = 4950 : 50 = 99

 Vậy 2A = 99

Answer 2

\(A=0,01+0,02+0,03+...+0,98+0,99\)

\(\Rightarrow100A=1+2+4+...+98+99\)

\(\Rightarrow100A=\frac{\left(99+1\right)99}{2}=4950\)

\(\Rightarrow2A=4950\div50=99\)