ANSWER:
The cost of two walnuts varies proportionality with weight.The equation is c = 2.5w
SOLUTION:
Given, the cost of two walnuts varies proportionality with weight a two pound bag costs $5, a five pound bag costs $12.50.
Let the proportionality constant be x.
According to the given information,
c = xw --- (1)
Where, c is cost in dollars.
x is proportionality constant
w weight of walnuts in pounds
Given that, a two pound bag costs $5
Here, c = 5 and w = 2
So, substitute above values in (1)
5 = x(2)
x =

x = 2.5
We have another case also, so let us check it also.
A five pound bag costs $12.50
Here, c = 12.50 and w = 5
So, substitute above values in (1)
12.5 = x(5)
x =
= 2.5
So the value of proportionality constant is 2.5
Hence, the equation is c = 2.5w