The cost of milk (an input for ice cream) decreases. The equilibrium price and the equilibrium quantity

When the cost of milk decreases, it becomes cheaper for ice cream producers to make ice cream. This is likely to increase the supply of ice cream as producers can now produce more at the same cost.

In terms of the supply and demand model, this is represented by a rightward shift of the supply curve.

At the same time, the demand for ice cream remains unchanged because the cost of milk doesn't directly affect the consumer's desire for ice cream.

As a result of the increased supply, the equilibrium price of ice cream is likely to decrease. This is because there is now more ice cream being produced than there is demand for it, so the price must decrease to encourage more consumption.

In terms of the equilibrium quantity, it is likely to increase. This is because at the lower price, more consumers are willing and able to buy ice cream, so the quantity demanded increases.

So, in conclusion, when the cost of milk decreases, the equilibrium price of ice cream is likely to decrease and the equilibrium quantity is likely to increase.