Nine students of a class contribute money towards a common fund. Seven of them contribute Rs 50 each, and the remaining two contribute Rs 50 and Rs 90 more than this amount respectively. What is the average contribution of the class of 9 students?

Introduction / Context:
This question involves average contribution when different students contribute different amounts. Seven students pay the same fixed amount and two students pay larger amounts. The task is to compute the average contribution over all nine students.

Given Data / Assumptions:
- There are 9 students in total. - Seven students contribute Rs 50 each. - One student contributes Rs 50 more than Rs 50, that is Rs 100. - Another student contributes Rs 90 more than Rs 50, that is Rs 140. - We must find the average contribution per student.

Concept / Approach:
Average contribution equals total amount contributed divided by number of students. We first find the sum contributed by the seven equal contributors and then add the two higher contributions. Dividing this total by 9 gives the required average, which will be a non integer value.

Step-by-Step Solution:
Step 1: Contribution of each of the seven students = Rs 50. Step 2: Total contribution of these seven students = 7 * 50 = Rs 350. Step 3: Eighth student contributes 50 more than 50, so contributes Rs 100. Step 4: Ninth student contributes 90 more than 50, so contributes Rs 140. Step 5: Total contribution of all nine students = 350 + 100 + 140 = Rs 590. Step 6: Average contribution = total contribution / number of students = 590 / 9. Step 7: 590 / 9 is approximately equal to 65.56 rupees.

Verification / Alternative check:
We can express 590 / 9 as a mixed fraction. Dividing 590 by 9 gives quotient 65 and remainder 5, so the exact average is 65 5/9 rupees. Converting 5/9 to decimal gives about 0.56, so 65.56 is a good approximation. Multiplying this approximate average back by 9 returns about 590, confirming consistency within rounding limits.

Why Other Options Are Wrong:
- 60 is lower than the base contribution of 50 plus the effect of higher contributors. - 70, 75 and 80 are too high and do not match the precise total of Rs 590. - Only approximately 65.56 matches total 590 when multiplied by 9.

Common Pitfalls:
Some learners mistakenly add 50 and 90 directly to the average or misinterpret the phrase more than this amount. Another common error is averaging the three distinct values 50, 100 and 140 without considering how many students pay each amount. Always calculate the total rupees first, then divide by the total number of contributors.

Final Answer:
The average contribution of the 9 students is approximately Rs 65.56.