Correct Answer: D

Rationale: To calculate a 10% tip on a bill of $28.40, you would first find 10% of $28.40, which is $2.84. Since you typically round up when leaving a tip, the estimated gratuity would be $3.00. Option A is incorrect as it is too high for a 10% tip. Option B is incorrect as it is too high. Option C is incorrect as it is too low for a 10% tip. Therefore, the correct answer is $3.00.

Correct Answer: A

Rationale: After one friend eats half of the pizza, the remaining half is divided equally among the three other friends. Each of the three friends receives 1/3 of the remaining half, not 1/6. Therefore, the correct answer is 1/3 of 1/2, which is 1/6 of the total pizza. The incorrect choices are: B. 1/3 - This is the correct portion of the remaining pizza each friend receives, not 1/3. C. 1/4 - This is not the accurate portion each friend receives after the first friend eats half of the pizza. D. 1/6 - This is the portion of the total pizza each friend receives, not the portion each friend receives after the initial half is consumed.

Correct Answer: A

Rationale: To convert Fahrenheit to Celsius, you start by subtracting 32 from the Fahrenheit temperature and then divide the result by 1.8. This formula accounts for the freezing point of water at 32°F and the conversion factor to Celsius. To convert Celsius to Fahrenheit, you multiply the Celsius temperature by 1.8 and then add 32. This process takes into consideration the conversion factor from Celsius to Fahrenheit and the freezing point of water. Choice B is incorrect as dividing by 2 instead of 1.8 would yield an inaccurate conversion. Choice C is incorrect as it involves incorrect operations for both conversions. Choice D is incorrect as subtracting 30 instead of 32 for Fahrenheit to Celsius and multiplying by 2 instead of 1.8 for Celsius to Fahrenheit would provide incorrect results.

Correct Answer: B

Rationale: The correct answer is B: 1. The average width of a doorway typically ranges from 0.8 to 1.2 meters, making 1 meter a reasonable estimate. Choice A (0.5) is too narrow for a standard doorway. Choice C (10) is too wide for a typical doorway. Choice D (3) is also wider than the standard width of a doorway.

Correct Answer: A

Rationale: The correct expression for the sum of three times a number and eight times a different number is given by 3x + 8y. This represents adding three times the variable x (3x) to eight times the variable y (8y). Choice B (8x + 3x) is incorrect as it represents adding eight times x to three times x, which is redundant. Choice C (3x - 8y) is incorrect because it represents subtracting eight times y from three times x, not their sum. Choice D (8x - 3y) is also incorrect as it represents subtracting three times y from eight times x, not their sum.