Đáp án + Giải thích các bước giải:
`b)`
`A=1/6*3/5-(-2 1/2):4%+0,12`
`=1/10-(-5/2):1/25+12/100`
`=1/10-(-5/2)*25+3/25`
`=1/10-(-125/2)+3/25`
`=1/10+125/2+3/25`
`=10/100+6250/100+12/100=6272/100=1568/25`
`B=1/(1*5)+1/(5*9)+1/(9*13)+1/(13*17)+...+1/(57*61)`
`=1/4(4/(1*5)+4/(5*9)+4/(9*13)+...+4/(57*61))`
`=1/4(1-1/5+1/5-1/9+...+1/57-1/61)`
`=1/4(1-1/61)=1/4*60/61=15/61`.