sir please help me in datagridview

i have data in excel .i want to import it in datagridview in c# .
1.
when i import that file the values in cells not in accurate format i.e 3.12 will be as 3.1222222.....
2.
when i send back after performing some operations on data to excel (export)
it miss many values i.e all decimal values not shown.
3.
sir how can i perform opperations on datagridview like... if i want to impose a condition that the coloumns whose values less then all other will be coloured.
sir plz reply me as soon as ..
thank u very much