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#33 Number triangles

set by Peter Rowlett

There are two ways (shown below) to arrange the numbers 1 to 3 in a triangular grid so the number at the top of the triangle is the (positive) difference between the two making up the base. (We can mirror each arrangement right-to-left, but won’t count these mirror images as different.)

Can you complete these grids (below), where each triangular grouping of three squares follows the same rule? The first two triangles use the numbers 1 to 6 and the third uses the numbers 1 to 10.

There are four ways to fill…