4.3.8 Overall Cost

Activity symbol Activity: The Price of Doing it Yourself

Now that I’ve determined how many rolls of insulation I need to buy, what will the total cost be of doing the job myself?

Hint symbol

Comment

Remember:

  • Each roll costs $9.
  • There is a “three-for-two” sale.
  • I will also need to buy some safety equipment.
Solution symbol

Answer

Since I purchased 20 rolls of insulation, I will be able to take advantage of the “three-for-two” sale. This means that for every three rolls I purchase, I only pay for two rolls. Recall that each roll costs $9. Thus, for every set of three rolls I purchase, I will be charged only equation left hand side dollar times nine multiplication two equals right hand side dollar times 18.

To determine how many times I will get to take advantage of the sale, we can use a picture.

Since there are six sets of three rolls, it will cost equation left hand side dollar times 18 multiplication six equals right hand side dollar times 108. Unfortunately, the two additional rolls won’t be on sale, so the insulation will cost equation left hand side sum with, 3 , summands dollar times 108 plus dollar times nine plus dollar times nine equals right hand side dollar times 126.

Don’t forget that the safety gear is $45. This puts the charges at equation left hand side dollar times 126 plus dollar times 45 equals right hand side dollar times 171.

4.3.7 Determining the Number of Rolls

4.3.9 Decision Time