Final answer:
To solve this problem, we use the concept of direct and inverse variation. We set up an equation and solve for the constant k. Then we substitute the given values to find the number of whites.
Step-by-step explanation:
To solve this problem, we can use the concept of direct and inverse variation.
Given that whites vary directly as yellows cubed and inversely as purples, we can set up the following equation:
whites = k × yellows^3 / purples
Using the information given in the problem, we can substitute the values and solve for the constant k:
250 = k × 5^3 / 8
Simplifying the equation, we get:
k = 250 × 8 / 5^3
Now, to find the number of whites when there are 7 yellows and 4 purples, we can substitute these values into the equation:
whites = (250 × 8 / 5^3) × 7^3 / 4
Calculating this expression will give us the final answer.