Correct Answer: B

Rationale: To find the volume of the triangular shelf, first calculate the area of the triangle (1/2 * base * height) which is (1/2 * 40 * 30) = 600 sq cm. Then, multiply this area by the depth of the shelf (600 * 25) = 15000 cu cm. Therefore, the volume of each shelf is 3750 cu cm. Choice A, C, and D are incorrect as they do not correctly calculate the volume based on the dimensions provided.

Correct Answer: A

Rationale: To solve the proportion 3:2 :: 24:x, we set up the equation 3/2 = 24/x. Cross multiply to get 3x = 48, then divide by 3 to find x = 16. Therefore, the correct answer is 16. Choice B (12) is incorrect as it does not satisfy the proportion. Choice C (2) is incorrect as it does not match the relationship between the numbers given. Choice D (22) is incorrect as it is not the solution to the proportion equation.

Correct Answer: C

Rationale: To find the difference between 15.7 and 9.8, you need to subtract 9.8 from 15.7. This operation results in 5.9. Therefore, the correct answer is 5.9. Choice A, 6.1, is incorrect as it represents the result of subtracting 9.8 from 15.9, not 15.7. Choice B, 8.96, is also incorrect as it is not the correct result of the subtraction provided. Choice D, 4.30, is incorrect as well, as it is not the result of subtracting 9.8 from 15.7.

Correct Answer: C

Rationale: The metric system is based on powers of 10, making calculations and conversions easier because each unit increases or decreases by a factor of 10.

Correct Answer: C

Rationale: To convert a fraction to a decimal, divide the numerator by the denominator. In this case, 5 · 8 = 0.625. Therefore, the correct answer is 0.625. Choice A (0.7) is incorrect as it represents 7/10, choice B (0.325) is incorrect as it represents 325/1000, and choice D (5.8) is incorrect as it is not the result of dividing 5 by 8.