Total Weight = Weight of the book + Weight of the CD + Weight of the box
Total Weight = 1 1/4 pound + 1/5 pound + 3/10 pound
Total Weight = 5/4 + 1/5 + 3/10
To add these fractions, you need to put them over a common denominator. To do that, find the least common multiple of 4, 5, and 10. Below is a table of the multiples. The least multiple they have in common is 20, shown in orange. So use 20 as your least common denominator.
1 2 3 4 5 6 7
4 x 4 8 12 16 20 24 ...
5 x 5 10 15 20 25 30 ...
10 x 10 20 30 40 50 60 ...
Can you finish it from here?