Mary ate 4 and 1/2

To find the total number of pears that Mary and Carmie ate, we need to add the two amounts together.

Mary ate \( 4 \frac{1}{2} \) pears, which can be converted to an improper fraction: \[ 4 \frac{1}{2} = 4 + \frac{1}{2} = \frac{8}{2} + \frac{1}{2} = \frac{9}{2} \]

Carmie ate \( 7 \frac{2}{4} \) pears. The fraction \( \frac{2}{4} \) simplifies to \( \frac{1}{2} \), so: \[ 7 \frac{2}{4} = 7 + \frac{2}{4} = 7 + \frac{1}{2} = \frac{14}{2} + \frac{1}{2} = \frac{15}{2} \]

Now, we can add the two amounts: \[ \frac{9}{2} + \frac{15}{2} = \frac{9 + 15}{2} = \frac{24}{2} = 12 \]

Thus, the total number of pears in the box is 12.