Answer :

[tex]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[/tex]

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.

⇒[tex]\text{unit rate per balloon} = \frac{2.5}{1} = 2.5[/tex] ft ribbon

Use conversion:

1 feet = 1/3 yard

then;

2.5 ft = 0.833333333 yard

⇒[tex]\text{unit rate per balloon} = \frac{2.5}{1} = 0.833333333[/tex] yard ribbon

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

[tex]\text{Number of ribbons} = \text{Unit rate per balloons} \times 18[/tex]

Substitute the given values we have;

[tex]\text{Number of ribbons} = 0.83333333 \times 18 = 15[/tex] yards

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