*Question G5C04:
What is the approximate total resistance of a 100- and a 200-ohm resistor in parallel?*  

*Correct Answer is  D: 67 ohms*  

### AI Response: (may contain errors)  

To find the total resistance of resistors in parallel, we use the formula:

$$
\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2}
$$

For this question, we have:
- $R_1 = 100 \, \text{ohms}$
- $R_2 = 200 \, \text{ohms}$

Substituting these values into the formula gives:

$$
\frac{1}{R_{total}} = \frac{1}{100} + \frac{1}{200}
$$

To combine the fractions, we find a common denominator, which is 200:

$$
\frac{1}{R_{total}} = \frac{2}{200} + \frac{1}{200} = \frac{3}{200}
$$

Now, we take the reciprocal to find $R_{total}$:

$$
R_{total} = \frac{200}{3} \approx 66.67 \, \text{ohms}
$$

Thus, the approximate total resistance is 67 ohms, which corresponds to choice D.

### Explanation of Choices:
- **Correct Answer (D: 67 ohms)**: This is the correct calculation for the total resistance of a 100-ohm and a 200-ohm resistor in parallel.
  
- **A: 300 ohms**: This choice incorrectly assumes that resistors in parallel add directly, which is not the case. In parallel, the total resistance is always less than the smallest resistor.

- **B: 150 ohms**: This choice might come from an incorrect average calculation or misunderstanding of the parallel formula. It does not apply to the parallel resistance calculation.

- **C: 75 ohms**: This choice is also incorrect. It may arise from a miscalculation or confusion with series resistance, where resistors add directly.

### Summary:
- Use the parallel resistance formula to find the total resistance.
- Remember that the total resistance in parallel is always less than the smallest resistor in the group.