In the month of September, the additional number of votes needed by A and B…

Concept: A quantity that is p% more than a reference value R equals R × (1 + p/100). When a group has to reach such a target, the extra amount it must still gain is the target minus what the group already holds: Extra required = R × (1 + p/100) − (current value). The reference R is always the quantity named after "more than", never the group's own total.

Application to the September figures:

1. Read the September row of the table: A polled 2.0 lakh votes, B polled 2.0 lakh votes and D polled 4.5 lakh votes.

2. Current combined strength of A and B = 2.0 + 2.0 = 4.0 lakh = 4,00,000 votes.

3. Reference value R = D's September votes = 4.5 lakh = 4,50,000 votes.

4. Target for A and B together = R × (1 + 7/100) = 4,50,000 × 1.07 = 4,81,500 votes.

5. Additional votes required = target − current = 4,81,500 − 4,00,000 = 81,500 votes.

Cross-check by a second route: A and B together trail D by 4,50,000 − 4,00,000 = 50,000 votes, and 7% of D is 0.07 × 4,50,000 = 31,500 votes. Closing the gap and then rising 7% above D needs 50,000 + 31,500 = 81,500 votes — the same figure, so the working is consistent.

Two slips to avoid: taking the percentage on the pair's own total (0.07 × 4,00,000 = 28,000), and treating "7% more than D" as though only 7% of D (31,500) were needed, which ignores the 50,000-vote gap A and B start with.