Lynne bought a bag of grapefruit, 1 5/8 pounds of apples, and 2 3/16 pounds of bananas. the total weight of her purchases was 7 1/2 pounds. how much did the bad of grapefruit weigh? give me the answer and show me how you do it!

The bag of grapefruit weighs 3 and 11/16
first: find a common denominator of 1/2, 5/8, and 3/16; 16 is the least common multiple.
16 divided by 2 is 8, so we multiply 1 by 8 and have 8/16
16 divided by 8 is 2, so we multiply 5 by 2 and have 10/16.
now, the three quantities given are 1 and 10/16, 2 and 3/16, and 7 and 8/16.
then, we subtract 1 and 10/16 from 7 and 8/16
  7 8/16
- 1 10/16
this is 5 and 7/8, or 5 and 14/16

then, we subtract 2 and 3/16 from 5 and 14/16 to get 3 and 11/16

there you have it :)