Question

 A 89:0,25+89:0 ,2+89

B 1/1*2 +1/2*3+1/3*4+...+1/9*10

/ là phần nhé ( phân số)

Answer 1

\(A=89:0,25+89:0,2+89\)

\(=>A=89\cdot4+89\cdot5+89\cdot1\)

\(=>A=89\cdot\left(4+5+1\right)\)

\(=>A=89\cdot10\)

\(=>A=890\)

\(B=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+.....+\frac{1}{9\cdot10}\)

\(=>B=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.....+\frac{1}{9}-\frac{1}{10}\)

\(=>B=1-\frac{1}{10}\)

\(=>B=\frac{10}{10}-\frac{1}{10}\)

\(=>B=\frac{9}{10}\)