Lucy is knitting a blanket and needs to buy some more yarn. At her local craft store, 2 skeins of yarn cost $7 and 8 skeins of yarn cost $28. What is the constant of proportionality in this direct variation?

A: 7/2

B:2/7

C:7

D:2

B. 7/2

Step-by-step explanation:

If 2 skeins of yard cost $7, and you buy 2 skeins for $7 4 times you will have bought 8 skeins at a final cost of $28, which is the second option you have for buying 8 skeins. Then, no matter hoy many skeins you are willing to buy, to know the price, you have to take into account that one skein worth $3.5 (7/2), and to know the price of multiples of skeins, you have to multiply 7/2 (=3.5) by the amount of skeins you want to buy.

The correct answer is A. 7/2

Step-by-step explanation:

Cost of 2 skeins of yarn at the local craft store = US$ 7

Cost of 8 skeins of yarn at the local craft store = US$ 28

What is the constant of proportionality in this direct variation?

Let's evaluate the first option:

Price per skein = Price / number of skeins

Price per skein = 7 / 2

Price per skein = US$ 3.50

Let's evaluate the second option:

Price per skein = Price / number of skeins

Price per skein = 28 / 8

Price per skein = US$ 3.50

As we can see the price is the same for both options, US$ 3.50, that expressed in a fractional number is 7/2. Therefore, the correct answer is A. 7/2