Which of the following numbers is a prime number? A. 2 B. 4 C. 6 D. 8

$$
30 + 70 = 100
$$
The sum is 100.  
**A. 100**

3 is in the thousands place.  
0 is in the hundreds place.  
8 is in the tens place.  
7 is in the ones place.

Three thousand eighty-seven.  
**B. Three thousand eighty-seven**

Factors of 12: $1, 2, 3, 4, 6, 12$

Factors of 18: $1, 2, 3, 6, 9, 18$

The common factors are $1, 2, 3, 6$. The greatest is 6.  
**A. 6**

Numbers: $2, 3, 4, 5, 6, 7, 8, 9$  
Prime numbers: $2, 3, 5, 7$  
**B. {2,3,5,7}**

$$
25\% = \frac{25}{100} = 0.25
$$

$$
0.25 \times 400 = 100
$$
**D. 100**

A. 2: Divisors are $1, 2$. It is a prime number.  
B. 4: Divisors are $1, 2, 4$. It is not a prime number.  
C. 6: Divisors are $1, 2, 3, 6$. It is not a prime number.  
D. 8: Divisors are $1, 2, 4, 8$. It is not a prime number.  
**A. 2**

Four thousand means 4 in the thousands place.  
Thirteen means 1 in the tens place and 3 in the ones place.  
There are no hundreds, so 0 in the hundreds place.

4,013  
**B. 4,013**

Even numbers: $2, 4, 6, 8$

$\{2, 4, 6, 8\}$  
**B. {2,4,6,8}**

A $360^\circ$ angle represents a full rotation. This is known as a reflex angle if it's an angle greater than $180^\circ$ but less than $360^\circ$. However, a full circle or a complete rotation is also $360^\circ$. Among the given options, a reflex angle is the closest description for an angle that can be $360^\circ$ in some contexts, though a full rotation is more precise. Given the options, a reflex angle is typically defined as an angle between $180^\circ$ and $360^\circ$. A full rotation is $360^\circ$. If the question implies an angle **whose measure is** $360^\circ$, it refers to a full rotation. None of the options perfectly describe a full rotation as a "figure". However, if we consider the **measure** of an angle, a reflex angle is the only option that can be close to $360^\circ$. Let's re-evaluate. A reflex angle is an angle that is greater than $180^\circ$ and less than $360^\circ$. A $360^\circ$ angle is a full rotation. None of the options are "full rotation" or "circle". If the question implies a type of angle, and $360^\circ$ is the measure, it's a full angle. Since "Reflex angle" is an option, and it's the largest type of angle listed, it's the most plausible choice if the question is slightly imprecise. However, a reflex angle is strictly less than $360^\circ$. Let's assume the question is asking for a type of angle that can be large, and $360^\circ$ is given as a measure. A full rotation is $360^\circ$. If we consider the options, none are a perfect fit for a $360^\circ$ angle. Let's consider if there's a typo and it meant to say "a full rotation". If we must choose from the given options, and knowing that a reflex angle is the largest type of angle listed, it's the most likely intended answer, despite the strict definition. Let's assume it's a full rotation.  
**D. Reflex angle** (Assuming the question implies a full rotation or the largest type of angle listed, though strictly a reflex angle is $<360^\circ$).

The digit '3' is immediately after the decimal point.

The first digit after the decimal point is in the tenths place.  
**A. Tenth place**

$$
324 \div 3 = 108
$$
**B. 108**

$$
3(2) - 2(3)
$$

$$
6 - 6
$$

$$
0
$$
**C. 0**

Factors of 16: $1, 2, 4, 8, 16$

A. 6: 6 is not in the list of factors of 16.  
B. 8: 8 is a factor of 16.  
C. 4: 4 is a factor of 16.  
D. 2: 2 is a factor of 16.  
**A. 6**

A. $20\% = 0.5$: $20\% = 0.20$. So, $0.20 \neq 0.5$. (Incorrect)  
B. $0.8 = 4/5$: Convert $4/5$ to a decimal. $4 \div 5 = 0.8$. So, $0.8 = 0.8$. (Correct)  
C. $10^3 = 300$: $10^3 = 10 \times 10 \times 10 = 1000$. So, $1000 \neq 300$. (Incorrect)  
D. $1/2 = 0.2$: $1/2 = 0.5$. So, $0.5 \neq 0.2$. (Incorrect)  
**B. 0.8 = 4/5**

Start from the rightmost digit (ones place): $3_{(4)} + 2_{(4)} = 5_{(10)}$.  
In base 4, $5_{(10)} = 1 \times 4 + 1 = 11_{(4)}$. So, write down 1 and carry over 1.

$2_{(4)} + 3_{(4)} + 1_{(carry)} = 6_{(10)}$.  
In base 4, $6_{(10)} = 1 \times 4 + 2 = 12_{(4)}$. So, write down 12.

The sum is $121_{(4)}$.  
**C. 121(4)** (or D, since C and D are identical)

$9, 6, 0, 1, 2, 8, 4, 3, 5, 7$

$0, 1, 2, 3, 4, 5, 6, 7, 8, 9$  
**C. 0,1,2,3,4,5,6,7,8,9**

$$
1 \frac{2}{3} = \frac{(1 \times 3) + 2}{3} = \frac{3+2}{3} = \frac{5}{3}
$$

$$
\frac{5}{3} \times \frac{9}{10}
$$

$$
\frac{\cancel{5}^1}{\cancel{3}^1} \times \frac{\cancel{9}^3}{\cancel{10}^2} = \frac{1 \times 3}{1 \times 2} = \frac{3}{2}
$$

$$
\frac{3}{2} = 1 \frac{1}{2}
$$
**B. 1 1/2**

Total students = 40  
Number of boys = 10  
Number of girls = $40 - 10 = 30$

Ratio of girls to boys = Number of girls : Number of boys
$$
30 : 10
$$

$$
30 \div 10 : 10 \div 10
$$
$$
3 : 1
$$
**C. 3:1**