Which of the following pairs of goods are complements, which are substitutes, and which are unrelated?
a. We observe the price of Jiffy peanut butter decreases and the quantity demanded of Smucker's strawberry jam increases:
b. A razor and a blade:
c. A Panasonic CD player and a JVC CD player:
d. You observe that your significant other adds 1oz of cream to each cup of coffee:

a. We observe the price of Jiffy peanut butter decreases and the quantity demanded of Smucker's strawberry jam increases:  COMPLEMENTS, since a decrease in the price of Jiffy peanut butter increased the quantity demanded of Smucker's strawberry jam.

b. A razor and a blade:  COMPLEMENTS, since they work together, a razor is useless without a blade and vice versa. An increase in the price of either of them should decrease the quantity demanded of both products, and vice versa.

c. A Panasonic CD player and a JVC CD player:  SUBSTITUTES, since an increase in the price of Panasonic CD players will increase the quantity demanded of JVC CD players.

d. You observe that your significant other adds 1oz of cream to each cup of coffee: COMPLEMENTS, both you and your significant other complement each other, and cream and coffee are married for life. An increase in the price of cream reduces the quantity demanded of coffee and vice versa.