IPMAT Indore 2026 · Quantitative Ability · Question 44

IPMAT Indore 2026 previous year question on Sequences and Series, with the answer and a step-by-step solution.

Sequences and SeriesAlgebraMultiple choiceMedium
A certain number of people contributed to a charity. The first person contributed one rupee. The rule for contribution was that the next person would contribute double the amount already raised. If the total money raised for the charity was 2187 rupees, then the number of people who contributed to the charity is
  1. A
    9
  2. B
    7
  3. C
    8
  4. D
    6
Pick an option, then check.
Answer & solution

Answer: Option C

Step 1 — track the running total, not the individual gifts. Each person gives twice what has already been raised, so after their contribution the total becomes

\text{old total}+2\times \text{old total}=3\times \text{old total}

The total triples with every new contributor.

Step 2 — list the totals.

People

Total

1

1={3}^{0}

2

3={3}^{1}

3

9={3}^{2}

k

{3}^{k-1}

Step 3 — solve.

{3}^{k-1}=2187={3}^{7}\Rightarrow k-1=7 \Rightarrow k=8

Answer: Option 3 — 8

Shortcut. Spot that the total forms a GP with ratio 3 — far cleaner than tracking what each person gives. Then just recognise 2187={3}^{7} and remember the first person corresponds to {3}^{0}, so add one.

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