David obtains 76, 65, 82, 67 and 85 marks out of 100 in English, Mathematics, Physics, Chemistry and Biology respectively. What are his average marks out of 100 across these five subjects?

Introduction / Context:
This question checks the basic concept of arithmetic mean, which is widely used to summarise marks in examinations. Understanding how to compute the average of a set of values is a foundational aptitude skill for many competitive exams.

Given Data / Assumptions:
- Marks in five subjects are 76, 65, 82, 67 and 85.
- Each subject carries 100 marks.
- All subjects are weighted equally in the average.
- We assume no subject is counted more than once.

Concept / Approach:
The average (arithmetic mean) of a set of observations is defined as:
Average = (Sum of all observations) / (Number of observations)
Here, the observations are the marks scored by David in the five subjects.

Step-by-Step Solution:
Step 1: Write down the marks: 76, 65, 82, 67, 85.Step 2: Find the sum: 76 + 65 + 82 + 67 + 85.Step 3: Compute the sum: 76 + 65 = 141, 141 + 82 = 223, 223 + 67 = 290, 290 + 85 = 375.Step 4: Number of subjects = 5.Step 5: Average marks = 375 / 5 = 75.

Verification / Alternative check:
You can approximate to verify: the marks are mostly around the low to mid seventies. Taking a rough average around that region, 75 is reasonable. A quick mental check of 5 multiplied by 75 gives 375, which matches the sum of the marks, confirming the calculation.

Why Other Options Are Wrong:
- 68: This would correspond to a much lower total of 68 * 5 = 340, which is less than the actual total of 375.
- 65: This is even lower, giving a total of 325, clearly not equal to the given sum.
- 60: This would give a total of only 300, far from 375, so it cannot be correct.

Common Pitfalls:
- Forgetting to include one of the subjects in the total sum can lead to an incorrect average.
- Dividing by the wrong number of subjects, for example dividing by 4 instead of 5, is another typical mistake.
- Some students mistakenly use the highest or lowest mark instead of computing the mean.

Final Answer:
The correct average marks scored by David across the five subjects is 75.