Thinkgeek is an online retailer that caters to computer enthusiasts and other "geeky" social groups. their merchandise includes clothing, electronic and scientific gadgets, unusual computer peripherals, office toys, pet toys, child toys, and caffeinated drinks and candy. thinkgeek runs a points-for-reward system called geek points, under which customers can earn rewards for buying more products. this is an example of segmentation by
a) demographic
b) benefit
c) aggregate
d) economic
e) usagerate

Alandlord rented an art studio to an artist. under the terms of the signed, written, two-year lease, the artist agreed to pay the landlord $1,000 per month and to assume responsibility for all necessary repairs. after the first year of the lease, the artist assigned the balance of his lease to a sculptor. the landlord approved the sculptor as a tenant and accepted two rent payments from her, and then the landlord sold the building to an investor. the sculptor had made two payments to the investor when an electrical fire broke out in the studio, injuring the sculptor. the fire was caused by faulty wiring. the landlord was aware that there was a dangerous wiring problem when he leased the property to the artist. but when the landlord discovered how costly repairs would be, he decided it would be more profitable to sell the property than to repair it. the problem was not easily discoverable by anyone other than an expert electrician, and the landlord did not tell the artist, the sculptor, or the investor about the problem. the sculptor sues to recover damages for her injuries. from whom can the sculptor recover?

Which of the following is a problem for the production of public goods?

Alarge tank is filled to capacity with 500 gallons of pure water. brine containing 2 pounds of salt per gallon is pumped into the tank at a rate of 5 gal/min. the well-mixed solution is pumped out at the same rate. find the number a(t) of pounds of salt in the tank at time t.