smc

Question

All the numbers 2, 3, 4, 5, 6, 7 are assigned to the six faces of a cube, one number to each face. For each of the eight vertices of the cube, a product of three numbers is computed, where the three numbers are the numbers assigned to the three faces that include that vertex. What is the greatest possible value of the sum of these eight products?

Accepted Answer

First assign each face the letters a,b,c,d,e,f. The sum of the product of the faces is abc+acd+ade+aeb+fbc+fcd+fde+feb. We can factor this into (a+f)(b+c)(d+e) which is the product of the sum of each pair of opposite faces. In order to maximize (a+f)(b+c)(d+e) we use the numbers (7+2)(6+3)(5+4) or 729.