He can make 3 batches of soup.
Starting with 10 pounds of tomatoes and taking out the number of pounds he sets aside for spaghetti sauce, 2.8, we have:
10-2.8 = 7.2 pounds left.
0.2 is read as "two tenths," so 7.2 = 7 2/10
We divide this remaining number of pounds by 2 2/5 for each batch of soup:
7 2/10 ÷ 2 2/5
Convert each to an improper fraction:
72/10 ÷ 12/5
Multiply by the reciprocal:
72/10 × 5/12 = 360/120 = 3
