Correct Answer: B

Rationale: There are 1,000 milliliters in 1 liter. The prefix 'milli-' means one-thousandth, so when converting from liters to milliliters, you multiply by 1,000.
Therefore, the correct answer is 1,000 mL.
Choice A (100 mL) is incorrect as it represents one-tenth of the correct conversion.
Choice C (500 mL) is incorrect as it is half of the correct conversion.
Choice D (50 mL) is incorrect as it is one-twentieth of the correct conversion.

Correct Answer: A

Rationale:
To add 12 1/21 and 3 1/3, first add the whole numbers: 12 + 3 = 15.
Then, add the fractions: 1/21 + 1/3.
To find a common denominator, multiply 21 by 3 to get 63. Convert 1/21 to an equivalent fraction with a denominator of 63 by multiplying the numerator and denominator by 3, resulting in 3/63. Now add 3/63 (equivalent to 1/21) and 21/63 (equivalent to 1/3) to get 24/63. Simplifying 24/63 gives 8/21.
Therefore, the sum is 15 8/21.

Choices B, C, and D are incorrect because they do not result from the correct addition of the given numbers and fractions.

Correct Answer: C

Rationale:
To add mixed numbers, first add the whole numbers together, then add the fractions. 6 + 8 = 14. For the fractions: 3/4 + 1/6 = (18 + 4) / 24 = 22/24 = 11/12.
Therefore, 6 & 3/4 + 8 & 1/6 equals 14 & 11/12.
Choice A is incorrect as it does not represent the correct sum.
Choice B is incorrect because it does not match the correct result.
Choice D is incorrect as it simplifies to 12 & 1/6, not 12 & 3/24.

Correct Answer: A

Rationale:
To determine how much weight Jenny has lost, you need to multiply the weight lost per month (3.2 lbs) by the number of months (6). 3.2 lbs x 6 = 19.2 lbs.
Therefore, Jenny has lost a total of 19.2 lbs.
Choice B (15 lbs) is incorrect because it does not account for the total weight lost over the 6 months.
Choice C (20 lbs) is incorrect as it overestimates the total weight lost.
Choice D (18 lbs) is incorrect as it underestimates the total weight lost.

Correct Answer: B

Rationale: The correct answer is B: 24m. The perimeter of a square is found by adding up all its sides. In this case, since the garden bed has a side length of 8 meters, the perimeter would be 8m + 8m + 8m + 8m = 24m.

Choices A, C, and D are incorrect because they do not correctly calculate the perimeter of a square with a side length of 8 meters.