Average of prime numbers: Find the average of all prime numbers between 60 and 90.

Introduction / Context:
The task is to list primes in the interval and compute their arithmetic mean. This checks prime identification and mean calculation skills.

Given Data / Assumptions:

• Interval: 60 to 90 inclusive of endpoints only if prime

Concept / Approach:
Enumerate primes, sum them, divide by count.

Step-by-Step Solution:

Verification / Alternative check:
Cross check primality quickly: none of the numbers are divisible by 2, 3, 5, 7 except as expected for composites; list is correct.

Why Other Options Are Wrong:

• 72, 74, 73.6: Do not equal the computed mean. 74.7 is the correct rounded value.

Common Pitfalls:
Missing a prime like 83 or including a composite such as 77 or 87 by mistake.

Final Answer: