Find the value of x in the ratio and proportion 18:x=10:300.

Correct Answer: D

Rationale: To find the value of x, cross multiply in the ratio 18:x=10:300. This gives 18 * 300 = 10 * x. Solving for x, x = 540. Therefore, the correct answer is D. Choice A (16), Choice B (180), and Choice C (30) are incorrect because they do not satisfy the proportion equation 18:x=10:300 when cross multiplied.

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 convert a percentage to a decimal, divide by 100. In this case, to convert 76.3% to a decimal, you move the decimal point two places to the left, resulting in 0.763. Therefore, the correct answer is C. Choice A (0.0763) is incorrect as it represents 7.63% as a decimal. Choice B (7) and Choice D (7.63) are not correct conversions of the given percentage to a decimal.

Correct Answer: A

Rationale: To solve the equation 3x - 5 = 10, start by isolating x. Add 5 to both sides of the equation to get 3x = 15. Then, divide by 3 on both sides to find x = 5. Therefore, the correct answer is x = 5. Choice B, x = 10, is incorrect because adding 5 to 10 does not yield 10. Choice C, x = 15, is incorrect as adding 5 to 15 does not equal 10. Choice D, x = 20, is incorrect because adding 5 to 20 does not result in 10.

Correct Answer: D

Rationale: To find the value of x in the given ratio and proportion, we can set up the equation as 15:2000=x:200. Cross multiply to get x * 2000 = 15 * 200. Simplifying this gives x = 1. Therefore, the correct answer is D, which is 1. Choice A (7), Choice B (0), and Choice C (7,777) are incorrect as they do not match the correct calculation of x.

Correct Answer: B

Rationale: To calculate the total number of balloons needed, multiply the number of children by the balloons each child will receive: 16 children * 15 balloons = 240 balloons. Since there are 50 balloons per packet, divide the total number of balloons needed by the balloons per packet: 240 balloons · 50 balloons per packet = 4.8 packets. As you cannot buy a fraction of a packet, the mother will need to round up to the nearest whole number of packets, which is 5. Therefore, the correct answer is 5 packets. Choice A (17) is incorrect because it does not accurately calculate the number of packets needed. Choice C (6) is incorrect as it overestimates the number of packets required. Choice D (50) is incorrect as it does not consider the number of children and balloons per child in the calculation.

Correct Answer: B

Rationale: 1 milliliter is approximately equal to 0.2 teaspoons. To find out how many teaspoons are in 0.8 milliliters, we can set up a proportion: 0.8 milliliters * 0.2 teaspoons/1 milliliter = 0.16 teaspoons. Since 0.16 teaspoons is not one of the answer choices, we need to convert it to a more practical measurement. The closest option is 0.4 teaspoons, making it the correct answer. Choice A, 0.2 teaspoons, is incorrect because 0.8 milliliters is more than that. Choices C and D, 0.6 teaspoons and 0.8 teaspoons, respectively, are also incorrect based on the conversion factor of 1 milliliter to 0.2 teaspoons.

Correct Answer: D

Rationale: To divide mixed numbers, convert them to improper fractions. 5 & 3/4 = 23/4 and 1/2 = 2/1. So, 23/4 · 2/1 = 23/4 * 1/2 = 23/8 = 2 & 7/8. Therefore, 5 & 3/4 divided by 1/2 reduces to 11 & 1/2. Choices A, B, and C are incorrect because they do not represent the correct result of dividing 5 & 3/4 by 1/2.