Which is the better buy, 7 pounds for $8.47 or 9 pounds for $11.07?

7 for 8.47 because 8.47/7=1.21 and 11.07/9=1.23

Let us take the case of 7 pounds for $8.47 first.

7 pounds of a product costs = 8.47 dollars

Then

1 pound of the same product will cost = (8.47/7) dollars

= 1.21 dollars

Now let us take the case of 9 pounds for $11.07

9 pounds of a product costs = 11.07 dollars

Then

1 pound of the same product will cost = (11.07/9) pounds

= 1.23 dollars

So from the above deductions we can see that 9 pounds for $11.07 is a better buy than 7 pounds for $8.47. I hope the procedure is clear enough for you to understand. In future you can use this method for solving similar problems.