This resource consists of two cross-number puzzles suitable for Grade 5 upwards. Geometric diagrams are given illustrating the first few triangular numbers. To solve both puzzles the student will need to calculate particular triangular numbers, The largest required is the 41st. Clues use a basic algebra subscript notation for each triangular number.
The Teachers Guide outlines three possible approaches to the completion of the worksheet ranging from "brute force" calculation to more investigative approaches involving the triangular number formula.
The answers to the puzzles are also supplied in the Teacher's Guide.