We have 25 students in the class, and each one will eat 2 brownies, then we must do the double of brownies for each student, or 50 brownies total.
If each batch makes 18 brownies, and we need 50 brownies, we need more than two batches because two batches will make 18*2 = 36 brownies, and we need 50 brownies, then let's see if 3 batches are enough, 3 batches will give
[tex]18\cdot3=54\text{ brownies}[/tex]54 brownies are more than the 50 brownies we needed. Therefore they need 3 batches!
