Correct Answer: A

Rationale: To add mixed numbers, convert them to improper fractions: 6 3/4 = 27/4 and 8 1/6 = 49/6. Then, add the fractions to get 27/4 + 49/6 = 162/24 + 98/24 = 260/24 = 21 20/24 = 21 10/12 = 21 5/6 = 14 11/12. Therefore, the correct answer is 14 11/12. Choice B (12 3/4) is incorrect as it does not match the correct calculation. Choice C (12 3/24) is incorrect due to the erroneous denominator in the final fraction. Choice D (14 2/5) is incorrect as it does not correspond to the correct sum of the fractions.

Correct Answer: A

Rationale: To produce 24 eggs in 24 hours, 4 times the number of chickens needed to produce 6 eggs is required. Since it takes 2 chickens to produce 6 eggs, 8 chickens are needed to produce 24 eggs in the same time frame. Choice B, 12 chickens, is incorrect because it doesn't consider the proportionality between chickens and eggs. Choice C, 18 chickens, is incorrect as it overestimates the number of chickens needed. Choice D, 6 chickens, is incorrect as it doesn't account for the increased number of eggs required.

Correct Answer: C

Rationale: Rationale: The correct answer is obtained by applying the formula for the circumference of a circle, which is \(C = \pi \times d\), where \(d\) is the diameter of the circle. By substituting the given diameter of 40cm into the formula and performing the calculation, we find that the circumference of the pizza is 125.6cm.

Correct Answer: D

Rationale: To find the distance traveled, multiply the speed of 70 mph by the time of 6 hours: 70 mph 6 hours = 420 miles. Therefore, the correct answer is 420 miles. Choices A, B, and C are incorrect as they do not result from the correct calculation.

Correct Answer: A

Rationale: Subtract the whole numbers and then subtract the fractions: 12 - 7 4\5 = 5 1\5.