Seven friends spend Rs 14 each on a project. An eighth friend spends Rs 21 more than the average expenditure of all eight friends. What is the total amount of money, in rupees, spent by all of them together?

Introduction / Context:
This question involves an unknown average where one of the contributors spends an amount defined relative to that average. We must set up an equation in terms of the average and then use it to compute the total expenditure.

Given Data / Assumptions:
- Seven friends each spend Rs 14. - There are 8 friends in total. - The eighth friend spends Rs 21 more than the average expenditure of all eight friends. - Let the average expenditure of all eight friends be A rupees.

Concept / Approach:
Total expenditure equals number of friends multiplied by the average, that is 8A. It also equals the sum of the amounts spent by the seven friends plus the amount spent by the eighth friend, which is A + 21. Equating these two expressions for the total gives a linear equation for A. Once A is found, the overall total can be calculated as 8A.

Step-by-Step Solution:
Step 1: Total spent by seven friends = 7 * 14 = 98 rupees. Step 2: Let average expenditure of all eight be A rupees. Step 3: Eighth friend spends A + 21 rupees. Step 4: Total expenditure T can be written as T = 98 + (A + 21) = 119 + A. Step 5: By definition of average, T is also equal to 8A. Step 6: Set 8A = 119 + A. Step 7: Rearrange: 8A - A = 119, so 7A = 119 and A = 17. Step 8: Total expenditure T = 8A = 8 * 17 = 136 rupees.

Verification / Alternative check:
Check the eighth friend expenditure. Eighth friend spends A + 21 = 17 + 21 = 38 rupees. Then total from eight friends is 7 * 14 + 38 = 98 + 38 = 136. Average = 136 / 8 = 17, which matches A. This confirms internal consistency.

Why Other Options Are Wrong:
- 133, 141, 147 and 155 lead to different implied averages that do not satisfy the condition that the eighth friend spends 21 more than that average.

Common Pitfalls:
Some learners treat the extra 21 rupees as added to 14 instead of to the average, or forget to include the eighth friend in the total count for the average. Others attempt guesswork instead of forming an equation. A clear definition of A and equating totals is the safest method.

Final Answer:
The total amount of money spent by the eight friends is Rs 136.