Formula

Formula

I need to use this formula but the formula field does not calculate this in the correct way
ex.
(Lunch_Number_3_5 *Serving_Amount_3_51) + (Lunch_Number_6_12  *  Serving_Amount_6_121) 
(10*1.5)+(1*2) = 17 but this is not what Im getting. Im getting 32. 
Any help Thank you