Correct Answer: A

Rationale: To calculate the area taken by the trees, we need to account for the space each tree requires. Each tree needs 5 meters of free space all around it, totaling 10 meters added to each dimension. Therefore, the new dimensions of the field are (650-10) meters by (780-10) meters. Calculating the area of the new field: (640m 770m = 492,800m²). To find the free area remaining, subtract the new field's area from the original field's area: 507,000m² - 492,800m² = 14,200m². Therefore, the free area left after planting the trees is 14,200m². Choice A is the correct answer as it represents the free area left after planting the trees.

Correct Answer: C

Rationale: To convert miles to feet, multiply the number of miles by the conversion factor of feet per mile. Since there are 5280 feet in 1 mile, to find the number of feet in 2 miles, you multiply 2 by 5280, resulting in 10560 feet. Choice A, 5280 feet, is the conversion factor for 1 mile, not for 2 miles. Choices B and D are incorrect calculations that do not follow the conversion factor correctly.

Correct Answer: C

Rationale: To convert teaspoons to milliliters, we use the conversion factor of 1 teaspoon = approximately 4.93 milliliters. Multiplying 2 teaspoons by 4.93 gives us 9.86 milliliters. Therefore, the correct answer is 9.86 milliliters. Choice A (4.3 milliliters) is incorrect as it doesn't align with the conversion factor. Choice B (9 milliliters) is incorrect because it doesn't consider the precise conversion factor. Choice D (4 milliliters) is incorrect as it doesn't account for the accurate conversion from teaspoons to milliliters.

Correct Answer: A

Rationale: To convert the fraction 7/8 into a decimal, you divide 7 by 8, which equals 0.875. To express this decimal as a percentage, you multiply it by 100 to get 87.5%. Choices B, C, and D are incorrect because they do not represent the correct conversion of the fraction 7/8 into a decimal and a percent.

Correct Answer: C

Rationale: To calculate the total area to be painted, find the area of each wall and the floor, sum them up, and subtract the area of the top surface of the pool. The area to be painted is (2*8 + 2*5 + 8*5) = 16 + 10 + 40 = 66 sq m. Since one can of paint covers 10 sq m, divide the total area (66 sq m) by the coverage area per can to determine the number of cans needed. Therefore, you need 88 sq m of paint, which is equivalent to 9 cans of paint. Choice A, B, and D are incorrect as they do not represent the correct calculation of the total area to be painted.