Verified Answer :

\(1yd=3ft\to1ft=\frac{1}{3}yd\\--------------------\\2.5ft\to1\ ballon\\\\therefore\\\\18\times2.5ft=45ft\to18\ ballons\\\\45ft=45\times\frac{1}{3}yd=\boxed{15yd}\leftarrow answer\)

Answer:

15 yards of ribbon does olivia need for 18 balloons

Step-by-step explanation:

Unit rate defined as the rates are expressed  as a quantity 1 such as 4 meter per seconds  or 5 miles per hours.

As pert the statement:

Olivia ties 2.5 feet of ribbon onto one balloon.

⇒\(\text{unit rate per balloon} = \frac{2.5}{1} = 2.5\) ft ribbon

Use conversion:

1 feet = 1/3 yard

then;

2.5 ft = 0.833333333 yard

⇒\(\text{unit rate per balloon} = \frac{2.5}{1} = 0.833333333\) yard ribbon

We have top find how many yards of ribbon does olivia need for 18 balloons

\(\text{Number of ribbons} = \text{Unit rate per balloons} \times 18\)

Substitute the given values we have;

\(\text{Number of ribbons} = 0.83333333 \times 18 = 15\) yards

Therefore, 15 yards of ribbon does olivia need for 18 balloons