if their is a dozen snack bars their are 3 friends     

   1 friend got 2.8 bars another friend got 2.7 bars the last friend got 2.5     

   how many snack bars are left ?     

 

   12 – (2.8 + 2.7 + 2.5)  =     

   12 – 8                         =  4     

   _.