Question

which is lighter? a grocery bag of bowling balls that is 2/5 full or a grocery bag of feathers that is 4/5 full?

Explanation:

Step1: Consider the nature of objects

Bowling balls are heavy, feathers are light.

Step2: Analyze the situation

Even though the bag of feathers is more full ($\frac{4}{5}$ vs $\frac{2}{5}$ of the bag), the weight per unit volume (or per ball/feather) of bowling balls is much greater than that of feathers. A small number (proportion $\frac{2}{5}$) of heavy - weight bowling balls will still be heavier than a larger number (proportion $\frac{4}{5}$) of very - light feathers.

Answer:

The grocery bag of feathers that is $\frac{4}{5}$ full is lighter.