Correct Answer: B

Rationale: The scale of 1:30 means that 1 inch on the plan represents 30 inches in actual size. If the width of the barn door on the plan is 3 inches, the actual width is calculated by multiplying 3 inches by the scale factor (30), giving 90 inches. To convert inches to feet, divide by 12 (since 12 inches = 1 foot), resulting in 90 inches · 12 = 7.5 feet. Therefore, the correct answer is 10 feet (option B), not 7.5 feet. Option A (90 inches) is the result before converting to feet, option C (9 feet) is the incorrect conversion if the initial calculation was done correctly, and option D (7.5 feet) is the incorrect conversion of the initial calculation.

Correct Answer: D

Rationale: To find Olivia's new salary after a 4% increase, we calculate 4% of $51,200, which is 0.04 x $51,200 = $2,048. Adding this increase to Olivia's current salary gives us the new salary: $51,200 + $2,048 = $53,248. Therefore, Olivia's salary after the 4% increase will be $53,248. Choices A, B, and C are incorrect as they do not reflect the correct calculation for the new salary after a 4% increase.

Correct Answer: C

Rationale: If a horse can trot around a track twice in 10 minutes, it completes one circle in 5 minutes. To determine how many times it will circle the track in half an hour (30 minutes), divide the total time by the time taken for one circle: 30 minutes / 5 minutes per circle = 6 times. Therefore, the horse will circle the track 6 times at the same speed in half an hour. Choice A, 3 times, is incorrect as it does not consider the correct time taken for a single circle. Choice B, 5 times, is incorrect as it miscalculates the total number of circles within half an hour. Choice D, 10 times, is incorrect as it overestimates the number of circles the horse can complete in the given time frame.

Correct Answer: A

Rationale: To find 40% of 150, you multiply 150 by 0.40 (which represents 40% in decimal form). This calculation results in 60. Therefore, choice A, 60, is the correct answer. Choice B (65), choice C (70), and choice D (85) are incorrect as they do not reflect the accurate calculation for finding 40% of 150.

Correct Answer: C

Rationale: To find the sum of 12 + 2 + 312, you simply need to add these numbers together. 12 + 2 = 14, and when you add 312 to 14, you get the correct total of 326. Therefore, the correct answer is C. Choice A (936), choice B (374.4), and choice D (318.24) are incorrect as they do not represent the correct sum of the given numbers.