giúp mk với các bạn ơi đang cần gấp lắm 
a, \(\dfrac{2483-13}{4966-26}=\dfrac{2483-13}{2\left(2483-13\right)}=\dfrac{1}{2}\)
b, \(\dfrac{2727-101}{7575+303}=\dfrac{2525+202-101}{2525.3+303}=\dfrac{2525+101}{25.101.3+303}\)
\(=\dfrac{25.101+101}{25.303+303}=\dfrac{101\left(25+1\right)}{303\left(25+1\right)}=\dfrac{101}{303}=\dfrac{1}{3}\)
c, \(\dfrac{2002}{2000.16-1970}\)
\(=\dfrac{2002}{2000.15+2000-1970}\)
\(=\dfrac{2002}{2000.15+30}\)
\(=\dfrac{2002}{2000.15+2.15}\)
\(=\dfrac{2002}{15\left(2000+2\right)}=\dfrac{2002}{15.2002}=\dfrac{1}{15}\)
d,\(\dfrac{1.2.3+2.4.6+4.8.12+7.14.21}{1.3.6+2.6.12+4.12.24+7.21.42}\)
\(=\dfrac{1.2.3+2.4.6+4.8.12+7.14.21}{1.3.2.3+2.6.4.3+4.12.8.3+7.21.14.3}\)
\(=\dfrac{1.2.3+2.4.6+4.8.12+7.14.21}{3\left(1.2.3+2.4.6+4.8.12+7.14.21\right)}\)
\(=\dfrac{1}{3}\)
BCNN(2,3,15,3) = 30
\(\dfrac{1}{2}=\dfrac{1.15}{2.15}=\dfrac{15}{30};\dfrac{1}{3}=\dfrac{1.10}{3.10}=\dfrac{10}{30};\dfrac{1}{15}=\dfrac{1.2}{15.2}=\dfrac{2}{30};\dfrac{1}{3}=\dfrac{1.10}{3.10}=\dfrac{10}{30}\)
K chắc lắm
a) \(\dfrac{2483-13}{4966-26}=\dfrac{13\left(191-1\right)}{26\left(191-1\right)}=\dfrac{13}{26}=\dfrac{1}{2}\)
b) \(\dfrac{2727-101}{7575+303}=\dfrac{101\left(27-1\right)}{101\left(75+3\right)}=\dfrac{26}{78}=\dfrac{2.13}{2.3.13}=\dfrac{1}{3}\)
c) \(\dfrac{2002}{2000.16-1970}=\dfrac{2002}{2000.16-2000+30}=\dfrac{2002}{2000\left(16-1\right)+30}=\dfrac{2002}{2000.15+30}=\dfrac{2002}{15\left(2000+2\right)}=\dfrac{2002}{15.2002}=\dfrac{1}{15}\)
d) \(\dfrac{1.2.3+2.4.6+4.8.12+7.4.21}{1.3.6+2.6.12+4.12.24+7.21.42}=\dfrac{1.2.3\left(1+2+4\right)+7.4.21}{1.3.6\left(1+2+4\right)+7.21.42}=\dfrac{2.3.7+7.4.21}{3.6.7+7.21.42}==\dfrac{2.3.7\left(1+2.7\right)}{3.6.7\left(1+7.7\right)}=\dfrac{2.15}{6.50}=\dfrac{2.3.5}{2.3.5.10}=\dfrac{1}{10}\)Nếu có sai sót gì thì mong bạn bỏ qua nha ! 
