1=1003

2=2215

7021 I_7

00          1003

    21

       0

 1003

+

 1212

 2215

Hok tốt

Đáp án :

  7021 : 7 = 1003

  1003 + 1212 = 2215

7/5+4/5   7/20-1/4         5/4x3/9      7/2 : 8

=7+4/5    =7/20-5/20      =5/4x1/3    =7/2x 1/8

=11/5       =7-5/20          =5/12         =7/16

                 = 1/10 

Nhớ tick đấy

đâu có biết tick...

\(\frac{1212}{1515}+\frac{1212}{3535}+\frac{1212}{6363}+\frac{1212}{9999}\)

\(=\frac{12}{15}+\frac{12}{35}+\frac{12}{63}+\frac{12}{99}\)

\(=12\cdot\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\)

\(=12\cdot\frac{4}{33}\)

\(=\frac{16}{11}\)

\(\frac{1212}{1515}+\frac{1212}{3535}+\frac{1212}{6363}+\frac{1212}{9999}\)

\(=\frac{12}{15}+\frac{12}{35}+\frac{12}{63}+\frac{12}{99}\)

\(=12\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\)

\(=12\left(\frac{1}{3\cdot5}+\frac{1}{3\cdot7}+\frac{1}{7\cdot9}+\frac{1}{9\cdot11}\right)\)

\(=12\cdot\frac{1}{2}\left(\frac{2}{3\cdot5}+\frac{2}{3\cdot7}+\frac{2}{7\cdot9}+\frac{2}{9\cdot11}\right)\)

\(=6\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)\)

\(=6\left(\frac{1}{3}-\frac{1}{11}\right)\)

\(=6\cdot\frac{8}{33}\)

\(=\frac{48}{33}\)

Sorry , mình làm hơi tắt 1 xíu

Ta có : \(12\cdot\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\)

\(=6\cdot\left(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+\frac{2}{99}\right)\)

\(=6\cdot\left(\frac{2}{3\cdot5}+\cdot\cdot\cdot+\frac{2}{9\cdot11}\right)\)

\(=6\cdot\left(\frac{1}{3}-\frac{1}{5}+\cdot\cdot\cdot+\frac{1}{9}-\frac{1}{11}\right)\)

\(=6\cdot\left(\frac{1}{3}-\frac{1}{11}\right)\)

\(=6\cdot\frac{8}{33}\)

\(=\frac{16}{11}\)

172 x 4 = 688   

214325 x 4 = 857 300