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1. ## OS math

Physical memory = 32 frames Certainly, we need 5 bits to select one of the frames. Besides, we also need 10 bits to identify one of the 2^10 positions within the frame . Physical address size = 15 bits
2. ## List all NP problems here

Be careful! Satisfability of boolean equations with more than 2 variables is NP-Complete! Satisfability of first order predicates is undecidable. 2-SAT is Polynomial.
3. ## OS math

Physical memory = 32 frames Logical memory = 8 pages x 1024 words Logical address points to 2 ^ 13 words. Therefore, it needs 13 bits. What about the physical address? Certainly, it needs 5 bits for the frame. But what's the size of each frame? One page has the same size as one frame? If so, physical address needs to address 2^10 positions within a frame. Physical address size = 15 bits
4. ## GRE tomorrow! passionate ideas: e-rater gave 4.0 (how to improve?)

Thank you very much! :tup:
5. ## Guideline for essay

The site is not available. :(

9. ## Test tomorrow! Accidents in the road: e-rater gave 5.0 (how to obtain 6.0?)

Hi People, My test is tomorrow. Please, I would like to know how to improve the composition below. E-Rater gave me a score of 5.0. The feedback was: - style: repetition of word ("accident") - organization and developmnet: e-rater has identified only one main idea. How should I clearly expose the three ideas in the composition? - statistics: 430 words, 22 sentences Best regards, Daniel Topic: Six months ago the region of Forestville increased the speed limit for vehicles traveling on the region's highways by ten miles per hour. Since that change took effect, the number of automobile accidents in that region has increased by 15 percent. But the speed limit in Elmsford, a region neighboring Forestville, remained unchanged, and automobile accidents declined slightly during the same six-month period. Therefore, if the citizens of Forestville want to reduce the number of automobile accidents on the region's highways, they should campaign to reduce Forestville's speed limit to what it was before the increase. Discuss how well reasoned you find this argument. Your Answer: The speed limit in the region of Forestville has recently been focus of critics. The author of a critic argues that the speed limit should be decreased. His argument is based on statistics that compare the number of accidents in Forsetville and Elmsford. However, his reasoning is not convincing, since (a) the statistics considered may be biased, (b) the author does not mention what is the speed limit in Elmsford and © there is no clear relationship of cause and effect between the speed limit and the number of accidents. Let us analyze each of these issues in details. First, the author presents statistics showing that the number of automobile accidents increased by 15 percent in Forestville during the last semester. But he does not mention what was the absolute number of accidents in Forestville and in Elmsford. This information is essential, since if the number of accidents in Elmsford used to be huge and the number of accidents in Elmsford is small, both a slight decline in the number of accidents in Elmsford and a 15 percent increase in the number of accidents in Forestville are insignificant. Second, the author mentions that "the speed limit in Elmsford (...) remained unchanged, and automobile accidents declined". Nevertheless, he does not mention what is the speed limit in Elmsford. It is possible that the Forestville increase of the speed limit was done so as to make it equal to the one used in Elmsford. In that case, it is possible that in the short run, during a period of adaptation, the number of car accidents in Forestville increased. In the long run, the number of car accidents may become stable, or even decrease. Third, it is possible that during the six months considered the number of accidents historically has been greater compared to the other semester. For instance, during winter the number of car accidents may increase because of snow. So, the author needs to give more data about how automobile accidents were distributed among the months during the last years. If the number of accidents usually increases by more than 15 percent during the six months considered, than the speed limit had a positive effect, and not the opposite. To sum up, the author argues that the limit speed for vehicles in Forestville should be decreased. However, he does not give adequate support to his argument, and that destroys its soundness. The statistics showed are incomplete, the comparisons made are nebulous and the implicit cause-effect relationship established is not clear. The author needs to reconsider these details in order to better support his theory.
10. ## Smile Bright toothpaste: E-rater gave 5.0 (how to improve it to 6.0?)

Topic: A recent survey of dental patients showed that people who use Smile-Bright toothpaste are most likely to have capped teeth---artificial but natural-looking protective coverings placed by dentists on individual teeth. Those people who had begun using Smile-Bright toothpaste early in life were more likely to have capped teeth than were people who had begun using Smile-Bright later in life. In addition, those who reported brushing their teeth more than twice a day with Smile-Bright toothpaste were more likely to have caps on their teeth than were those who reported brushing with Smile-Bright less frequently. Therefore, people wishing to avoid having their teeth capped should not use Smile-Bright toothpaste. Discuss how well reasoned you find this argument. Your Answer: The author concludes that people should avoid using Smile-Bright toothpaste if they don't want to have their teeth capped. His reasoning is based on the statistics relating the frequency of usage of the Smile-Bright toothpaste and the likeliness of having capped teeth. Altough the ideas are clearly stated, the argument is not convincing because the source of the data presented is not mentioned, the relation between the causes and effects showed are not evident and nothing is stated about non Smile-Bright toothpastes. Let us consider each of these aspects in details. First, the statistics presented may be biased. The author does not mention how many people were interviewed, how frequently have they used the Smile-Bright toothpaste, and when did they started using it. He uses vague expressions, such as "later in life" and "early in life" to describe those who have used the toothpaste in the short run and in the long run, respectively. Besides that, the author implies that there is a relation of cause and effect between using the Smile-Bright toothpaste and having teeth capped. However, nothing is stated in order to support this theory. The fact that more people who used Smile-Bright had their teeth capped may be caused by lots of reasons. For instance, those who use Smile-Bright toothpaste may be more concerned with their health and teeth. Therefore, they go more frequently to dentists, and have a greater probability of having their teeth capped. In addition, the author does not discuss the differences between the Smile-Bright toothpastes and the other toothpastes. It is not clear that other toothpastes would cause less harm to the health than the Smile-Bright toothpaste. Indeed, the other toothpastes may have chemical substances that are even worse compared to those contained in the Smile-Bright toothpaste. To sum up, the author argues that Smile-Bright toothpaste should not be used so as to avoid having the teeth capped. However, he does not give proper arguments to support the fact that Smile-Bright toothpastes are the real causes of having the teeth capped. He also doe not discuss the properties of other kinds of toothpastes available in the market. Therefore, more data needs to be collected in order to better understand what are the pros and cons of the Smile-Bright toothpaste, and to give a final judgement about whether it should be avoided or not.
11. ## Playing cards

Another approach: ( 13C4 + 13C4 + 13C4 + 13C4 ) / ( 52C4 ) 4 . ( 13 . 12 . 11 . 10 ) / ( 4 . 3. 2 ) _______________________________ = ( 52 . 51. 50. 49 ) / ( 4 . 3. 2 ) = ( 12/51 ) ( 11/50 ) ( 10/49 ) Another approach: 52 x 51 x 50 x 49 ways of selecting 4 cards 52 x 12 x 11 x 10 ways of selecting 4 cards of the same suit answer = 52 x 12 x 11 x 10 _______________ = 52 x 51 x 50 x 49 12 x 11 x 10 _____________ 51 x 50 x 49
12. ## A set problem

bf + bc + fc = (number of people that play exactly two sports) + 3 (number of people that play three sports) = (number of people that play at least two sports) + 2 (number of people that play three sports) = 8 + 2 x 1 = 8 + 2 = 10
13. ## Can anyone help me solve this math problem?

where is the circle?
14. ## A set problem

Another approach: Use the inclusion/exclusion principle http://mathworld.wolfram.com/Inclusion-ExclusionPrinciple.html n = b + f + c - ( bf + bc + fc ) + bfc + none n = 20 + 30 + 25 - ( 8 + 2 ) + 1 + none = 67 none = 67 - 75 + 10 - 1 = 1
15. ## Some problems from the forum members of 2004

Thanks. I've corrected it. ;)
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