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UKMT Junior Kangaroo, 2017

Algebra Difficulty 2.0 Junior Find the answer United Kingdom

Jacob and Zain take pencils from a box of $21$ pencils without replacing them. On Monday Jacob takes $\frac{2}{3}$ of the number of pencils that Zain takes. On Tuesday Jacob takes $\frac{1}{2}$ of the number of pencils that Zain takes. On Wednesday morning the box is empty. How many pencils does Jacob take?

(A) $8$ (B) $7$ (C) $6$ (D) $5$ (E) $4$

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