How to write numbers with fractions

 From:  mickelsen
3089.1 
How do you write numbers with a whole part and fractional part such as two and a half? If I put 2-1/2 then MoI interprets the dash as a minus sign and subtracts the 1/2 from the 2. If I put 2_1/2 I just get an error. There must be a way but I haven't been able to find it. Can someone help?
Thanks,
Mark