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UKMT Grey Kangaroo, 2022

Combinatorics Difficulty 2.0 Junior Find the answer United Kingdom

Several points were marked on a line. Renard then marked another point between each pair of adjacent points on the line. He performed this process a total of four times. There were then 225 points marked on the line. How many points were marked on the line initially?

(A) $15$ (B) $16$ (C) $20$ (D) $25$ (E) $30$

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