Rounddown

I want to add two cells that are calculated by a formula that divides data from another cell by 30. The cells have all been formated to display only 2 decimal places. When I sum the two cells it adds 0.13 and 0.13 with the result of 0.27. Obviously it is using additional decimal places in the original two cells and rounding the results to 0.27 rather that 0.26. How do I rounddown the sum?

______J______________
48 4 =SUM(J48/30)
50 4 =SUM(J50/30)
51 8 =SUM(K48:K50)