Correct Answer: C

Rationale: To convert a decimal to a percent, you multiply by 100 or move the decimal point two places to the right. In this case, 0.64 becomes 64%. Therefore, the correct answer is 64%. Choice A, 0.64%, is incorrect because it does not convert the decimal to a percent. Choice B, 6.4%, is incorrect as it mistakenly moves the decimal point only one place. Choice D, 0.064%, is incorrect as it moves the decimal point three places instead of two.

Correct Answer: A

Rationale: To find 18% of 600, you multiply 600 by 0.18, which equals 108. Since 108 is already a whole number, when rounding to the nearest whole number, it remains the same. Choices B, C, and D are incorrect as they do not represent the correct calculation for finding 18% of 600.

Correct Answer: B

Rationale: To convert a percentage to a decimal, you divide the percentage by 100. Therefore, 38% as a decimal is 0.38 (38 · 100 = 0.38). Choice A, 3.8, is incorrect as it is equivalent to 380%. Choice C, 0.038, is incorrect as it represents 3.8%. Choice D, 38.0, is incorrect as it is still in percentage form.

Correct Answer: D

Rationale: To find the total perimeter, we first calculate the perimeter of the semicircle, which is half of a full circle, so the formula is π * radius. For the semicircle with a radius of 2m, the perimeter is approximately 3.14 * 2m = 6.28m. Next, we calculate the perimeter of the rectangular section by adding twice the length and twice the width (2 * length + 2 * width). For the rectangle with dimensions 5m by 3m, the perimeter is 2 * 5m + 2 * 3m = 10m + 6m = 16m. Finally, we sum the perimeters of the semicircle and the rectangle to get the total perimeter: 6.28m + 16m = 22.28m. Rounding to the nearest meter, the total perimeter is approximately 22m. Therefore, the correct answer is 22m. Choices A, B, and C are incorrect as they do not accurately calculate the total perimeter of the playground fence.

Correct Answer: C

Rationale: The metric system is based on powers of 10, making calculations and conversions easier because each unit increases or decreases by a factor of 10.