how do I know how to find the constant of the proportianlity

Question

Lance is knitting a blanket and needs to buy some more yarn. At his local craft store, 2 balls of yarn cost $5 and 8 balls of yarn cost $20. What is the constant of proportionality in this direct variation situation?

A. 5/2
B. 2/5
C. 5
D. 2

Answer 1

To find the constant of proportionality, we can set up a proportion using the given information:

2 balls of yarn cost $5
8 balls of yarn cost $20

We can set up the proportion as follows:

2/8 = 5/20

To simplify this equation, we can cross multiply:

2 * 20 = 8 * 5

40 = 40

Since both sides of the equation are equal, we can see that the constant of proportionality is 5.

Therefore, the correct answer is C. 5.