OG 12th Problem Solving 201-215

Question 201 – “If m is the average (arithmetic mean) of the first….”
There is a faster way than the OG Method. In an evenly spaced set (we have consecutive multiples here), the median is equal to the mean. So the median minus the mean must equal 0.
Khan Academy Question 215 – 2.50

Question 202 – “If m > 0 and x is m percent of y, then, in terms of m,…”
OG Explanation is okay – easier to plug in numbers here.
Let x = 20 m = 40 and y = 50. That is, 20 is 40% of 50. The question is y is what percent of x. y is 50 and x is 20 so y is 250% of x, so are answer should be 250 when m is plugged in.
Answer choice A: 100(40) = 4,000 INCORRECT
Answer choice B: 1/(100(40)) = 1/4000 INCORRECT
Answer choice C: 1/40 INCORRECT
Answer choice D: 10/40 = .25 INCORRECT
Answer choice E: 10,000 / 40 = 250 CORRECT
The answer is E
Question 216 Khan Academy 5.45

Question 203 – “What is the 25th digit to the right….”
OG Explanation is fine.\
219 Khan Academy – Begins at 3.30

Question 204 – “John and Mart were each paid x dollars in advance…”
OG Explanation is fine. Alternatively we could pick numbers. Let’s set the hourly rate to $1 per hour. John worked for 10 hours and should receive $10 and Mary worked for 8 hours and should receive $8. Let’s say there were each paid $9 and Mary gave $1 to John to make the hourly rates the same. John was paid $9 in advance and y=1. Thus the answer is 9y.
220 Khan Academy Begins at 5:00

Question 205 – “In the rectangular coordinate systems above….”
OG Explanation is okay. Since P = (4,0) and O = (0,0), it follows that OP is 4. Since R is on the axis, we have a right triangle. So let 4 be the base. For the area to be 12, the height must be 6 because ½(4)(6)=12.
Khan Academy Question 222 – 1.40

Question 206 – “Car A is 20 miles behind Car B which is traveling in the same direction….”
OG Explanation is fine.
223 Khan Academy 3.35

Question 207 – “For the past n days, the average…..”
OG Explanation is fine; if you want to you can jump to the answer choices and test them out.
224 Khan Academy 5.55

Question 208 – “If x does not equal 0 and x does not equal 1 and if x is replaced….”
OG Explanation is okay but I think picking numbers is better. Let x=2, the expression evaluates to (3/-1) = 9. Plug in to see which answer choices give out 9 when x = 2.
225 Khan Academy 7.50

Question 209 – “In the figure above, if z=50 ….”

226 Khan Academy 0.00

Question 210 – “In the coordinate system above, which of the following is the……..”
OG Explanation is okay. Alternatives: if you remember Algebra, the slope of a line in standard form is –a/b. The slope is -2/3 here as the slope is downward slope and is 3 wide for being 2 high. Choice B is the only choice with slope -2/3. You could also plug in the points (0,2) and (3,0) and if both fit, that is the right answer choice.
227 Khan Academy 3.10

Question 211 – “If a two-digit positive integer has its digit reversed….”
OG Explanation is okay. Alternative you could try picking numbers till you got one that worked. I got 36 and 63.
228 Khan Academy Link – 2.30

Question 212 – “The circle with center C shown above is tangent to both….”
OG Explanation is fine.
229 Khan Academy 4.50

Question 213 – “In an electric circuit, two resistors with resistance x and y are connected…”
OG Explanation is fine.
Khan Academy Question 230 – Begins at 7:00

Question 214 – “Xavier, Yvonne, and Zelda, each try independently to solve a problem….”
OG Explanation is good. Notice, that answer choice A is 11/8 which is greater than 1 and an impossible probability.
Khan 231 – Begins 8.30

Question 215 – “If 1/x – 1/x+1 = 1/x+4 “
OG Explanation is okay. I think the easier way is to go directly to the answer choices. Because we can’t divide by 0, by looking at the denominators in the problem we can eliminate 0, -1, and -4 from the answer choice. Testing x = -2 and x = -3, we can verify that x = -2 is a solution.
232 Khan Academy Begins at 0.00

One Response to OG 12th Problem Solving 201-215

  1. praneetha says:

    I am not able to view videos for sum 214,215 and 216. it shows the same video of sum 209 again instead.

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