Answer:
She can make 2.2 Necklaces, and needs 3.5 more inches of string.
Explanation:
Let's carefully read the problem for information we need.
3 Friends, 4.5 Inches per friend. She only has 10 inches.
If each necklace is 4.5 inches, we need
4.5 (friend one) + 4.5 (friend 2) + 4.5 (friend 3). We can also just take 4.5 * 3 friends and get the same result. This equals 13.5.
But wait! We only have 10 inches... Jessica needs 3.5 more inches of string to be able too complete the 3rd necklace. This is the answer to "How much more string does she need to buy"
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For "How many necklaces can she make". Well, we know she can't make a full 3 necklaces. We can find out the answer to this by dividing the 10 inches she does have, by the 4.5 inches it takes to make one necklace.
10/4.5=2.2
This means she could make 2 necklaces, and 2/10 (.2) of another necklace before she runs out of string.