Given a strip of 10 equilateral triangles, how many folds are necessary to reduce it to a single equilateral triangle? You may only fold along the grid lines. Multiple folds along collinear segments are not counted as one fold. Here's an illustration of a 10 triangle strip, for reference:
Here is a solution that does it in 6 folds using colinear folds. Without, it would be 8.
First, fold along the halfway line
This takes us down to 9 visible triangles. Next we fold along the end trapezoidal shape.
We are down to 7 visible triangles. Folding along the long central edge...
Brings us to 5. Folding either of the inner lines...
Gives us 4 triangles, and easy symmetry makes the last two steps clear.