What is the estimated cost for 7.8 pounds of potatoes at 3.89

I am assuming you forgot to type the rest of the question ($3.89 per pound).  If that is not the question, then my answer will most likely be wrong.

First, set up the proportion.  Then, cross multiply and isolate the variable to solve.

3.89(7.8) = 1(x)

    30.34 = x

$30.34

The estimated cost for 7.8 pounds of potatoes is $30.34.

Step-by-step explanation:

Hi, to solve this problem we have to analyze the information given.

Assuming that 3.89 is the cost per pound, we have to multiply the cost per pound by the quantity (7.8 pounds).

So, mathematically speaking:

In conclusion, the estimated cost for 7.8 pounds of potatoes is $30.34.

Feel free to ask for more if it´s necessary or if you did not understand something.