In a large aquarium, there are 7 starfish for every 5 sea horses.

(a) Write the ratio of starfish to sea horses.
(b) If there are 15 sea horses in the large aquarium, how many starfish are there?

1 answer

(a) The ratio of starfish to sea horses is given as 7 starfish for every 5 sea horses. Therefore, the ratio can be expressed as:

\[ \text{Ratio of starfish to sea horses} = 7:5 \]

(b) If there are 15 sea horses, we can use the ratio to find the number of starfish. The ratio of starfish to sea horses is 7:5, meaning for every 5 sea horses, there are 7 starfish.

Let \( x \) be the number of starfish. We can set up a proportion based on the ratio:

\[ \frac{7}{5} = \frac{x}{15} \]

Now we can cross-multiply to solve for \( x \):

\[ 7 \cdot 15 = 5 \cdot x \ 105 = 5x \ x = \frac{105}{5} \ x = 21 \]

Thus, if there are 15 sea horses, there are 21 starfish in the aquarium.