A decorative box has a rectangular base (20cm by 15cm) and a hemispherical top with the same diameter as the base. What is the total surface area of the box (excluding the base)?

Correct Answer: C

Rationale: To find the total surface area of the box excluding the base, calculate the lateral surface area of the rectangular base and the surface area of the hemisphere. The lateral surface area of the rectangular base is 2(20cm x 15cm) = 600 sq cm. The surface area of the hemisphere is 2πr^2, where r is half the diameter of the base, so r = 10cm. Thus, the surface area of the hemisphere is 2π(10cm)^2 = 200π sq cm ≈ 628.32 sq cm. Add the lateral surface area of the base and the surface area of the hemisphere: 600 sq cm + 628.32 sq cm ≈ 1228.32 sq cm. Therefore, the total surface area of the box is approximately 1228.32 sq cm, which is closest to 1325 sq cm (Choice C). Choices A, B, and D are incorrect as they do not represent the accurate calculation of the total surface area of the box.

Correct Answer: D

Rationale: To express the repeating decimal 0.7777... as a fraction, let x = 0.7777... Multiplying both sides by 10 to shift the decimal point to the right gives: 10x = 7.7777... Subtracting the original equation from the new equation eliminates the repeating decimal: 10x - x = 7.7777... - 0.7777... 9x = 7 x = 7/9. Therefore, the decimal 0.7777... can be expressed as the fraction 7/9. Choices A, B, and C are incorrect as they do not accurately represent the decimal 0.7777... when converted to a fraction.

Correct Answer: B

Rationale: To convert 98.6 degrees Fahrenheit to Celsius, you can use the formula (98.6 - 32) 5/9. By solving this equation, the temperature is calculated to be 37°C. Therefore, the correct answer is B, 37 Celsius. Choice A, 35 Celsius, is incorrect because it is not the outcome of the conversion formula. Choice C, 38 Celsius, is incorrect as well, as it does not match the correct conversion result. Choice D, 36.5 Celsius, is also incorrect as it does not correspond to the accurate conversion from 98.6 degrees Fahrenheit.

Correct Answer: B

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: B

Rationale: To convert grams to kilograms, you need to divide by 1000 since there are 1000 grams in a kilogram. Therefore, 2000 grams is equal to 2 kilograms (2000 grams · 1000 = 2 kilograms). The correct answer is B: 2 kilograms. Choice A, 20 kilograms, is incorrect because multiplying by 10 (not dividing by 1000) would give that result. Choice C, 5 kilograms, and Choice D, 10 kilograms, are also incorrect as they do not correctly convert grams to kilograms.