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# Tutor profile: Rachel D.

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Rachel D.
Medical School Student
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## Questions

### Subject:Basic Chemistry

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Question:

One basic problem you will come across when beginning chemistry is learning to balance chemical equations. Here is a simple example. Note the number on the right side of the chemical symbols should be subscripts. Balance the equation: Fe + O2 → Fe2O3

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Rachel D.

A balanced equation means we need the same number of atoms on the reactants (left) side and products (right) side. Currently, on the reactant side we have: 1 Fe & 2 O, and on the product side 2 Fe & 3 O. To balance this we'll follow start with balancing atoms present in a single molecule of reactant and product first. So, let's balance the O (oxygen) first. Since we have three O's on the right side and only two O's on the left, we need to find the lowest common multiple - because remember, we cannot change the subscripts. So let's add a coefficient of 3 on O of the left side and a 2 in front of the Fe2O3: Fe + O2 → Fe2O3 turns into: Fe + 3O2 → 2Fe2O3 So now the number oxygen molecules is balanced on both sides at six on each side. Let's focus on the Fe (iron). We still only have one Fe molecules the left side but now we have four on the right side (because of the subscript of 2 and the coefficient in front of 2). All we need to do is add a coefficient of 4 in front of the Fe on the left side. Then our equation becomes: 4Fe + 3O2 → 2Fe2O3 We have balanced our chemical equation because we have 4 Fe molecules and 6 O molecules on each side of the arrow.

### Subject:English

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Question:

One element of the English language that is quite difficult is grammar. Here is an example of a question you may have on a grammar exam: True narcolepsy is the sudden and irresistible onset of sleep during waking hours. True narcolepsy is extremely dangerous. Please choose the sentence that best combines the above sentences. a. While true narcolepsy is the sudden and irresistible onset of sleep during waking hours and is extremely dangerous. b. The sudden and irresistible onset of sleep during waking hours, which is true narcolepsy but extremely dangerous. c. True narcolepsy is the sudden and irresistible onset of sleep during waking hours, yet narcolepsy is extremely dangerous. d. True narcolepsy is the sudden and irresistible onset of sleep during waking hours, and it is extremely dangerous.

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Rachel D.

So if you cannot identify the correct answer initially, go through knock out improbable answers. First, choice A is wrong because it is a sentence fragment. Choice B also makes no sense. Now we're left with C or D. Choice C prepares the reader for a contrast but fails to deliver: narcolepsy is occurs in both main clauses. Then we're left with choice D. The conjunction "and" in this sentence indicates "also" and therefore is the correct choice.

### Subject:Algebra

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Question:

Here's an example of a basic problem we might solve in algebra: 3x - 11 = 5x + 9 Solve for x.

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Rachel D.

So, the way we work through this is to first remember two basic rules: 1) We want to have all like terms on the same side, which means that the constant terms (the -11 and the 9) are on side and the variable terms (3x and 5x) are on the other. 2) Whatever we do to one side of the equation we have to do to the other side. We'll start with rule #1 and separate the like terms. We'll get all the variable terms on the right side first by subtracting 3x from each side of the equation: 3x - 11 = 5x + 9 -3x -3x -11 = 2x + 9 Now, we'll get all the constants on the left side by subtracting 9 from each side. Remember a negative minus an number is the same as a negative plus a negative: 3x - 11 = 5x + 9 -9 -9 -20 = 2x Then, we're left with: -20 = 2x. So to solve for x we divide both sides by 2 and get: -10 = x. So x= -10.

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