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VMO 1990 — Division A Question 3

VMO · VMO 1990 — Division A

Question 3

A tetrahedron is to be cut by three planes to obtain a parallelepiped whose three faces through one vertex lie on faces of the tetrahedron.
(a) Can the parallelepiped have volume $9/10$ of the tetrahedron's volume? Explain.
(b) Determine a common point of the three cutting planes so that the parallelepiped has volume $11/50$ of the tetrahedron's volume.