Based on sales data over the past year, the owner of a DVD store devises the demand function D(p) = 40 - 2p, where D(p) is the number of DVDs that can be sold in one day at a price of p dollars.

a. According to the model, how many DVDs can be sold in a day at price of $10?

b. According to the model, what is the maximum price that can charged (above which no DVDs can be sold)?

c. Find the elasticity function for this demand function.

d. For what prices is the demand elastic? Inelastic?

e. If the price of DVDs is raised from $10.00 to $10.25, what is the exact percentage decrease in demand (using the demand function)?

f. If the price of DVDs is raised from $10.00 to $10.25, what is the approximate percentage decrease in demand (using the elasticity function)?