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UKMT Pink Kangaroo, 2018

Algebra Difficulty 2.0 Junior Find the answer United Kingdom

Abdul wrote down four positive numbers. He chose one of them and added it to the mean of the other three. He repeated this for each of the four numbers in turn. The results were 17, 21, 23 and 29. What was the largest of Abdul's numbers?

(A) $12$ (B) $15$ (C) $21$ (D) $24$ (E) $29$

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