1? 4 =10 2? 5 = 14 6? 10 = 40 9? 11 = 30 1? 10 = ?

Geometrically, m ? n represents the number of objects in a trapezoidal array with m objects in the top row and
n objects in the bottom row. Algebraically we have

m ? n = m + (m+1) + (m+2) + ... + n.

Thus we have

1 ? 4 = 1 + 2 + 3 + 4 = 10
2 ? 5 = 2 + 3 + 4 + 5 = 14
6 ? 10 = 6 + 7 + 8...