which of the following numbers is the greatest common factor gcf of 12 and 18
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HESI A2

HESI A2 Math

1. What is the greatest common factor (GCF) of 12 and 18?

Correct answer: C

Rationale: The greatest common factor (GCF) of two numbers is the largest number that divides both numbers without leaving a remainder. To find the GCF of 12 and 18, we factorize each number: 12 = 2 x 2 x 3 and 18 = 2 x 3 x 3. The common factors are 2 and 3. The GCF is the product of these common factors, which is 6. Therefore, 6 is the greatest common factor of 12 and 18. Choice A (2) and Choice B (3) are factors of both numbers but not the greatest common factor. Choice D (9) is not a factor of both 12 and 18, making it incorrect.

2. What is the meaning of the word duration as used in the last paragraph?

Correct answer: B

Rationale: The word "duration" in the context of sleep refers to the length of time that children should sleep. It suggests a focus on the amount of sleep necessary for healthy development, making option B the correct choice as it aligns with the emphasis on recommended sleep hours for children.

3. A decorative box has a rectangular base (20cm by 15cm) and a hemispherical top with the same diameter as the base. What is the total surface area of the box (excluding the base)?

Correct answer: C

Rationale: To find the total surface area of the box excluding the base, calculate the lateral surface area of the rectangular base and the surface area of the hemisphere. The lateral surface area of the rectangular base is 2(20cm x 15cm) = 600 sq cm. The surface area of the hemisphere is 2πr^2, where r is half the diameter of the base, so r = 10cm. Thus, the surface area of the hemisphere is 2π(10cm)^2 = 200π sq cm ≈ 628.32 sq cm. Add the lateral surface area of the base and the surface area of the hemisphere: 600 sq cm + 628.32 sq cm ≈ 1228.32 sq cm. Therefore, the total surface area of the box is approximately 1228.32 sq cm, which is closest to 1325 sq cm (Choice C). Choices A, B, and D are incorrect as they do not represent the accurate calculation of the total surface area of the box.

4. Which is a triatomic allotrope of oxygen?

Correct answer: A

Rationale: Ozone (O3) is a triatomic allotrope of oxygen. It differs from the common diatomic oxygen molecule (O2) by having three oxygen atoms bonded together. Ozone is known for its protective role in the Earth's atmosphere, absorbing most of the Sun's harmful ultraviolet radiation. Water (H2O) is a compound composed of two hydrogen atoms and one oxygen atom. Acidic oxide and carbon dioxide are not triatomic allotropes of oxygen. Carbon dioxide consists of one carbon atom and two oxygen atoms, while acidic oxides refer to compounds where oxygen is bonded with other elements to form oxides, and they are not allotropes of oxygen.

5. Which word in the sentence needs to be corrected for proper grammar?

Correct answer: B

Rationale: The word 'A' should be corrected to 'an' in the sentence. The sentence should read, 'The nurse made an error with the medication, so the doctor made notes about it in the patient's file.' The article 'an' is used before a noun beginning with a vowel sound, like 'error' in this case. Choices A, C, and D are grammatically correct in the sentence and do not need to be altered.

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