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Tutor profile: Lesley M.

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Lesley M.
Biology Researcher
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Questions

Subject: Biology

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Question:

In one taxonomic classification, Archaea, Eukarya, and Bacteria represent the three major domains of life. Eukarya utilize the general transcription factors TBP (TATA-binding protein) and TFIIB in transcription, whereas Bacteria do not. At least one member of Archaea has a protein similar to TBP and a protein similar to TFIIB. Based on the observation, which of the following scenarios is most likely? A. Archaea and Eukarya diverged after their common ancestor diverged from Bacteria. B. Archaea and Bacteria diverged after their common ancestor diverged from Eukarya. C. Bacteria and Eukarya diverged after their common ancestor diverged from Archaea. D. Archaea, Eukarya, and Bacteria diverged simultaneously from a common ancestor. E. Archaea, Eukarya, and Bacteria each evolved from different ancestral organisms.

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Lesley M.
Answer:

The key phrase in this question is "most likely." In other words, we are looking for the most parsimonious explanation for this scenario. Parsimony is a principle in which the phylogeny of a group of species is assumed to be the pattern that requires the smallest number of evolutionary changes. We can weed of E because all life on Earth shared one common ancestor. D is also unlikely because there would need to be two changes that happen in the phylogeny that leads to the observation (two separate events arise in Eukarya and Archaea). Answers B and C also involve two changes along the phylogeny tree. That leaves us with answer A. In the case of answer A, only one change has to occur in the common ancestor of Archaea and Eukarya in order to see this observation.

Subject: ACT

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Question:

The list of numbers 41, 35, 30, X, Y, 15 has a median of 25. The mode of the list of numbers is 15. To the nearest whole number, what is the mean of the list? A. 20 B. 25 C. 26 D. 27 E. 30

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Lesley M.
Answer:

In order to calculate the mean of the list, we must first identify what X and Y are. We are given that the mode is 15. Because there is only one 15 in the given list, we can reasonably conclude that at least one of the unknown values is 15. For now, we will leave the other unknown number as it is and call it Y. So now we have this list: 41, 35, 30, 15, Y, 15. The median--which is defined as the middle number in a sorted, ascending or descending, list of numbers--is 25. Since there is an even number of values, we will eventually calculate the median by getting the average between the two middle values. First, we will rearrange the numbers so that it goes from least to greatest. 15, 15, 30, 35, 41 (with Y to the side). We know just looking at this list that Y cannot be the lowest, greatest value, 2nd greatest, or 2nd lowest because the averages don't much up to 25. Therefore, we can assume that Y is in the middle before 30 (notice how it can't be put after 30 because a number greater than 30 will give us a median greater than 25). Now, we can solve for Y. (Y+30)/2=25 Y+30=50 Y=20 Finally, we can calculate the mean by adding all the numbers and dividing the sum by the number of values in the list. (15+15+20+30+35+41)/6=26. The answer to this problem is C.

Subject: Algebra

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Question:

Find the distance between the points (-21,-4) and (13,41).

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Lesley M.
Answer:

The distance between any two points is given by the distance formula: d=sqrt[(x2-x1)^2+(y2-y1)^2]; where d is the distance between the two points (x1, y1) and (x2, y2). To find the distance between (-21,-4) and (13,41), simply plug the values into their respective place in the equation. d=sqrt[(13-(-21))^2+(41-(-4))^2]; d=sqrt[(34)^2+(45)^2] d=sqrt{1156+2025) d=56.40 Notice how if we switched the values for x1 and x2 and y1 and y2, we would still get the same answer as a result of the square function. d=sqrt[(-21-(13))^2+(-3-(41))^2]; d=sqrt[(-34)^2+(-45)^2] d=sqrt{1156+2025) d=56.40

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