Among the axioms mistaken for fact by the revenue managers of most airlines is the idea that changes in fuel prices affect all competitors in a given market equally. In fact, prices—and therefore profits—fluctuate unpredictably, offering competitive advantages for some airlines and disadvantages for others. For example, a more well-established airline with an aging fleet will experience lower fuel efficiency per mile than a newer company that has invested in the latest technology, meaning fuel represents a larger percentage of the established airline's operating costs. Moreover, airlines that negotiate and lock in fuel prices with suppliers in advance enjoy stabilized expenses and efficient planning; at the same time, they may lose cost savings when market rates drop unexpectedly during the contract period. In addition, the advantages of low fuel prices are greater for those airlines whose business models focus on minimizing costs than for those with high operating budgets and higher prices for consumers. Carriers with highly efficient logistics and operations, for example, may find that falling fuel costs allow them to profitably fly routes that were previously not cost-effective, such as short routes between small cities, generating low profit margins but also increasing the size of their markets. By understanding that they have multiple options and that not all airlines experience the same effects of the volatile fuel market, airline revenue managers can offer their companies an optimized operating strategy by familiarizing themselves with the fuel market and adapting their fuel procurement plans to their business models.

     In Lemon v. Kurtzman (1971), the Supreme Court ruled that the state of Pennsylvania could not subsidize religious private schools through its Nonpublic Elementary and Secondary Education Act. Although the funds allocated in the Act were limited to the purpose of reimbursing the schools for textbooks, instructional materials, and the salaries of teachers who did not teach religion, the Court held that since the Act had the result of benefiting primarily Roman Catholic schools, it overextended the government's power on behalf of a religious organization. Later cases have referred to the benchmark three-part test established by Lemon, which states that a U.S. law violates the Establishment Clause of the Constitution if (1) the purpose of the law is not a secular purpose, (2) the law's primary effect is to inhibit or further the practice of religion, or (3) the law creates “excessive entanglement” between government and religious authority.

     Other states have also faced questions concerning whether or not a government policy or activity violates the Constitution's prohibition on the establishment of religion. For example, in Pawtucket, Rhode Island, the inclusion of a religious symbol among secular holiday decorations in a display sponsored and maintained by the city, at minimal expense, was declared constitutionally permissible. Although the religious symbol was erected on government property, it was both a longstanding tradition in the town and appeared among other, purely secular, symbols of the holiday season; it had gone unchallenged in the courts for more than 40 years. This, however, did not prevent application of the “Lemon test.” Indeed, as the Supreme Court has interpreted it, the question of establishment of religion is often a matter of perception and context as much as it is of clear divisions. This flexible approach is illustrated by Lynch v. Donnelly (1984), in which the Court demonstrated that differing circumstances could indeed lead to different results of application of the “Lemon test.” Therefore, the Court ruled that, in Pawtucket's context, the appearance of a religious symbol amid various secular ones in a government-sponsored display did not violate the Constitution.

     It is a counterintuitive but well-documented historical truth that the economies of the classical cultures typically seen as the progenitors of western liberalism and political freedom were all founded on the development and perpetuation of agrarian slavery. Because the cultures of antiquity are often associated with Periclean democracy and Roman republicanism—both oligarchical political systems at least nominally dedicated to principled and representative rule—students of history are often confused to learn that the populations of these societies contained large numbers of disenfranchised individuals who were often indentured to members of the middle and upper classes for a lifetime of brutal servitude.

     Many historians attribute this confusion to the triumphalist mythmaking of previous generations of scholars of classical history; indeed, most interpretations of classical literature and history have been distorted, but one would nonetheless expect modern revisionism and understanding of the concept of presentism to provide balance.

     Historians note that there is little discussion of slavery or its moral significance within classical sources, seemingly because individuals in the classical period saw it as both an economic necessity and inherent to the world's natural order. They cite the example of the writer Heraclitus (535 B.C.E.–475 B.C.E.), a pre-Socratic philosopher. Heraclitus is known as the “Weeping Philosopher,” and he was among the most incisive thinkers working in antiquity but, even so, the omnipresent institution of slavery struck him as an immutable element of human affairs; he wrote that “War is the father of all, the king of all … he turns some into slaves and sets others free,” implying that slavery is beyond the power of political determination—and beyond intellectual moralizing. Heraclitus is not alone in his failure to question the moral underpinnings of a slave society. Aristotle, too, suggested that the taking and keeping of slaves was a component of natural law, a fundamental consequence of military activity rather than a conscious policy that could be actively perpetuated or proscribed by the laws of man. In promoting this view, though, Aristotle demonstrates an unusual degree of circumspection, wondering whether the taking of slaves could be justified if the war in which they were acquired was itself “unjust.” The figures of early modernity saw themselves as heirs to the classical tradition and inherited the Greek and Roman attitudes toward slavery and citizenship as well as their commitments to democracy and rational inquiry, and modern historians have, in their studies of these times, endeavored to avoid the interpretive trap of imposing their modern ethics on the people of ancient times.

     Bernard Winkler's analysis of the effect of the industrialization of England on the conduct of British foreign policy through the course of the nineteenth and early twentieth centuries is a major contribution to a scholarly debate pitting two separate schools of historical thought against each other: the school of economic determinism and the school of ideological determinism.

     Winkler makes the assertion that economic and technological developments play a decisive role in military mobilization and logistical organization. Stated more simply, economic development makes extensive foreign interventions inevitable by making them simpler. Winkler implies this phenomenon has been obfuscated by a recent fondness on the part of historians for ideological explanations, of which George Nguyen's is a representative example. For Nguyen, the economic possibility of a foreign action is insignificant compared to ethnic, religious, or socio-political motivations for pursuing a course of action abroad. Economic development is construed as a mere facilitator of extant international grievances and desires such as border disputes, enmity between competing religious sects, and long-term foreign policy goals. This contention represents a significant trend in academic historiography, and it is known as ideological determinism.

     Ideological determinists entrench themselves by embracing a mistaken interpretation of economic determinism: for example, economic determinists are supposed to contend that economic development is responsible for all the various subtleties of foreign policy implementation. The alternative to ideological determinism, to say it another way, is to see economics as coextensive with society, as being responsible for even the most minor variations in social phenomena.

     Winkler undermines the misrepresentations of the ideological determinists by means both conceptual and concrete. Conceptually, he defines “economic causes” according to the interactions of industrialization with extant political and sociological realities. Descriptions of sociological and political phenomena as wholly divorced from economic factors are untenable because a state can hardly feed its armies on ideas alone. On a more concrete level, Winkler shows that rapid advances in economic production opened new vistas for political interpretation, religious expression, international relations, and the organization of armies. Some developments Winkler attributes to the ways politicians and bodies politic reacted to the new realities of industrialization, whereas others are attributed to industrialization itself. Therefore, Winkler responds to the question: “When are economic causes decisive and when are the interpretations of changing economic realities more significant?”

     Koltsov predicted in 1927 that an organism's inherited traits are determined by gradual changes in a “giant hereditary molecule,” later known as DNA, that is the building block of the genome that determines an organism's genetic makeup. This hypothesis was unproven, for a time, because of limitations in experimental methodology and an inability to do much more than observe qualities of an organism's DNA compared to the traits it expressed.

     To determine the nature of the connection between DNA and heritable characteristics, scientists needed to be able to bring about changes in the genome and observe whether they corresponded to physical changes in the organism. An experiment conducted by Zimmer in 1935 indicated that this was possible: radiation applied to living tissue can change the structures of DNA and another nucleic acid, RNA, that are found in the cells of every organism. Most of the exposed molecules go unchanged in this experiment, but some of them respond to experimental pressures. When X-rays are applied to cells, the nucleic acids warp and rearrange themselves, sometimes dramatically altering the traits they cause the organism to express. Because the changes induced by radiation exposure are more rapid and intense than those brought about by natural selection, significantly altered heritable traits can be observed in a single generation.

    As a proof of the connection between DNA and heritable characteristics, radiation experiments have two advantages. First, they are universally applicable: the genome of any organism responds to radiation exposure in a way comparable to any other organism. Second, it is a more direct means of genetic intervention than other methods like selective breeding. These advantages mean that radiation experiments can be used to isolate the hereditary influence of DNA from other confounding variables. The results of these experiments demonstrate that DNA exerts a substantial influence on the hereditary characteristics organisms express: DNA is the way that organisms transfer heritable traits between generations. These experiments have established an unassailable connection between intergenerational biological change and the information contained within the building blocks of the genome.

    However, it is important to note that there are other biological mechanisms, such as epigenetics and certain environmental pressures, that also affect the expression of inherited characteristics. The advantage of the Koltsov theory is its broad applicability; DNA is present in every organism on earth, which is not true of the various other factors that might have a role to play in determining the expression of heritable characteristics. That said, the comparative immeasurability of these other potential influences does not make them unworthy of study.

     The general theory of relativity posits that major events in the universe, such as the creation of a black hole, create ripples in the space-time continuum, also known as gravitational waves, which were recently detected for the first time by the Laser Interferometer Gravitational Observatory (LIGO). Though the interferometer was invented in 1887, not until 2002 was one used in an attempt to detect gravitational waves. The instrument splits a laser beam so that the two resulting beams travel down perpendicular arms—perfectly identical tubes that are four kilometers long—then hit mirrors and return to their shared origin point. This allows the instrument to detect extremely minute changes in the lengths of the arms. In the absence of a gravitational wave, the wavelengths of the two beams match up perfectly. However, if something interferes with the beams' paths, their peaks and valleys no longer align, and the instrument registers the interference.

     Gravitational waves cause space to shrink in one direction and expand in a perpendicular direction. If the interferometer is hit by a gravitational wave, one arm will grow and the other will shrink by normally imperceptible amounts, but the differing distances traveled by the laser beams are registered by the instrument. The LIGO actually consists of two interferometers, thousands of kilometers apart, which compare data in order to rule out localized vibrations and flickers. In September 2015 it detected its first gravitational wave, which was determined to have been generated by the collision of two black holes between one and two billion years ago. Another gravitational wave was detected in December 2015.

efg

If , what is the value of ?

If and , is divisible by 5?

(1) z = 3

(2)

Carl's pet rabbit finishes a 2-pound bag of feed every 8 days. When Carl's rabbit and guinea pig both share the same bag of feed, they finish it in 5 days. How many days would it take Carl's guinea pig to finish a 2-pound bag by itself?

If is a prime number, is

divisible by ?

(1) and

(2)

Joseph bought nails for each, hooks for each, and screws for each. Joseph bought a total of items and paid a total of . If Joseph bought twice as many nails as screws, how many hooks did he buy?

A whale's length can be divided into three sections: its head, midsection, and tail. A certain whale has a head that is 50 feet long and a tail whose length is equal to the length of its head plus half the length of its midsection. If the whale's midsection is half the total length of the whale, how long is the whale?

When Jacob closes the drain in his bathtub and turns on the cold water spigot, it takes him 3 minutes and 40 seconds to fill the tub completely. If he fills it from the hot water spigot instead, it takes him 5 minutes and 30 seconds to fill it completely. When the drain is opened in a completely full bathtub, it takes 11 minutes for the tub to empty. How many minutes will it take Jacob to fill the bathtub with both hot and cold water running simultaneously, if the drain is open and draining at a constant pace?

What is the value of ?

(1)

(2) is a prime number

A shopkeeper purchased footballs at $10 per football and sold them at a price equal to the purchase price plus a markup. If the markup was 10% of the selling price, what was the shopkeeper's profit in dollars, to the nearest cent, on each football?

Which of the following equations describes a line parallel to the line below?

People who tend to hoard money and valuables often do not think of the interest that would be generated if a part of their wealth would have been invested in another form.

How many numbers in a set of 5 consecutive positive integers are divisible by 4?

(1) The median of the set is odd

(2) The mean of the set is prime