On a visit to sea spectacular, an outdoor aquarium, your nephew notices that each time a dolphin performs a trick it is rewarded with a fish. you have read the brochure that explains that the dolphins are trained this way to ensure that they will continue to perform the tricks for several performances each day. this is an example of:

Dr. dow jones wants to know whether a problem-based approach to teaching economics will result in higher academic performance than his traditional method. of the six sections of economics 101 at his university, dr. jones randomly assigns three sections to the traditional method and three sections to the problem-based method for unit 1 of the course. then all sections switch the instructional method for unit 2. he plans to compare the performance of the two groups of sections on their unit 1 and unit 2 exams. this study employs a design.

Areal estate agent is considering changing her cell phone plan. there are three plans to choose from, all of which involve a monthly service charge of $20. plan a has a cost of $.42 a minute for daytime calls and $.17 a minute for evening calls. plan b has a charge of $.52 a minute for daytime calls and $.15 a minute for evening calls. plan c has a flat rate of $80 with 275 minutes of calls allowed per month and a charge of $.38 per minute beyond that, day or evening.a. determine the total charge under each plan for this case: 150 minutes of day calls and 70 minutes of evening calls in a month. (do not round intermediate calculations. round your answer to 2 decimal places. omit the "$" sign in your response.)c. if the agent will use the service for daytime calls, over what range of call minutes will each plan be optimal? (round each answer to the nearest whole number.include the indifference point itself in each answer.)d. suppose that the agent expects both daytime and evening calls. at what point (i.e., percentage of total call minutes used for daytime calls) would she be indifferent between plans a and b?

An allergy products superstore buys 6000 of their most popular model of air filters each year. the price of the air filters is $18. the cost of ordering and receiving shipments is $12 per order. accounting estimates annual carrying costs are 20% of the price. the supplier lead time is 2 days. the store operates 240 days per year. each order is received from the supplier in a single delivery. there are no quantity discounts. what is the store’s minimum total annual cost of placing orders & carrying inventory?