Correct Answer: D

Rationale: The tree grows at an average rate of 4.2 inches per day. To find the rate of change per month, multiply the daily growth rate by the number of days in a month (30 days): 4.2 inches/day 30 days = 126 inches per month. Therefore, the rate of change in the tree's height is 126 inches per month, making option D the correct answer. Option A is incorrect because it miscalculates the rate based on daily growth. Option B is incorrect as it doesn't account for the total days in a month. Option C is incorrect as it overestimates the monthly growth rate.

Correct Answer: A

Rationale: To multiply fractions, multiply the numerators together and the denominators together. Multiplying 3/5 by 5/7 gives (3*5)/(5*7) = 15/35. This fraction simplifies to 3/7 by dividing the numerator and denominator by their greatest common factor, which is 5. Therefore, the correct answer is 3/7. Choices B, C, and D are incorrect as they do not result from multiplying 3/5 by 5/7.

Correct Answer: B

Rationale: From Equation 1: 2x + y = 0. Solve for y: y = -2x. Substitute y = -2x into Equation 2: x - 2(-2x) = 8. Simplify to x + 4x = 8, then 5x = 8, and x = 8 · 5 = 1.6. Substitute x = 1.6 back into y = -2x to find y = -3.2. Therefore, one solution is (1.6, -3.2). To find the second solution, use -1.6 for x to get (-1.6, 3.2). Thus, the correct answer is B, representing the solutions (1.8, -3.6) and (-1.8, 3.6). Choices A, C, and D contain incorrect values that do not match the solutions derived from solving the system of equations.

Correct Answer: A

Rationale: To multiply fractions, multiply the numerators together and the denominators together. For (3/5) * (5/8), you get (3*5) / (5*8) = 15 / 40, which simplifies to 3/8. Therefore, the correct answer is A. Choice B (3/5) is incorrect as it is one of the original fractions being multiplied. Choice C (15/40) is the result of the multiplication but not simplified to its lowest terms. Choice D (3/30) is incorrect as the numerator is not the result of multiplying 3 and 5 together.

Correct Answer: A

Rationale: The absolute value of x is equal to 10 when x is either -10 or 10. Therefore, the correct answer is A. Choices B, C, and D are incorrect because they do not satisfy the equation |x| = 10. For choice B, -11 and 11 do not satisfy the condition. Choices C and D also do not provide solutions that meet the equation's requirement.