1.Tim so nguyen to lon nhat co 3 chu so sao cho so do chia het cho a-b; c-d; e-f; a/b=125/35; c/d=144/30;e/f=56/24
2. C=1001. (2/12012+74/555555+2/13.7.11.5)
D=(1.2+2.3+3.4+...+2012.2013)-(2.2+3.3+4.4+...+2013.2013)
3.Tìm số tự nhiên có 6 cs sao cho: abcdef=3.abc.def
4. Cho doan AB=7cm. Tren tia AB lay I sao cho BK=2cm
a. chung minh rang: I nam giua A va K
b. Tinh IK