Question

For every 3 wrapped packages Mary uses 1/2 roll of wrapping paper how many packages can she wrap with 2 1/2 rolls of wrapping paper

Answer 1

She can wrap 15 packages :)

Answer 2

3 packages = 1/2 roll
? packages = 2 1/2 rolls

if 1/2 of a roll can wrap 3 packages, that means 1 roll can wrap 6 packages.

1/2 roll = 3 packages
1 roll = 6 packages
2 rolls= 12 packages

so to find how many packages can be wrapped with 2 1/2 rolls,

1/2 roll (3 packages) + 2 rolls (12 packages) = 2/12 rolls (15 packages)

15 packages can be wrapped using 2/12 rolls of paper.