Correct Answer: A

Rationale: A common denominator is a shared multiple of the denominators in a set of fractions. It is necessary when adding or subtracting fractions to have a common denominator to ensure that the fractions can be combined accurately. Choice B is incorrect because the common denominator is related to the denominators, not the numerators. Choice C is incorrect because while the common denominator is the same in all fractions being added or subtracted, it is not necessarily a number that is the same in all fractions. Choice D is incorrect because a common denominator is a multiple of the denominators, not a number that divides evenly into both fractions.

Correct Answer: B

Rationale: The correct way to find the factors of a number is to identify all pairs of numbers that, when multiplied together, result in the given number. This method allows you to determine all the factors of the number. Choice A is incorrect because dividing the number by all possible numbers is not an efficient way to find its factors. Choice C is incorrect as listing all the multiples of the number does not give the factors. Choice D is unrelated to finding factors as adding the digits of a number together does not provide information about its factors.

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: D

Rationale: After deducting $172 weekly for taxes ($72 + $35 + $65), the teacher's net weekly income is $558. Over 4 weeks, the total income is $2,232.00. Choice A is incorrect as it does not account for the taxes deducted. Choice B is incorrect as it overestimates the income by not deducting the taxes. Choice C is incorrect as it also does not consider the tax deductions.

Correct Answer: A

Rationale: The correct way to find the least common multiple is to list all the multiples of each number and then identify the smallest common multiple. Choice A is correct because it describes the correct process. Listing factors, as suggested in choice B, helps in finding the greatest common factor, not the least common multiple. Dividing the largest number by the smallest, as mentioned in choice C, does not help find the least common multiple. Multiplying the two numbers together, as stated in choice D, results in their least common multiple when the numbers have no common factors.