In the given figure, find the total number of straight lines.

In a “count the straight lines” figure, count each maximal straight line — one that runs unbroken from one boundary point of the figure to another — exactly once, even where other lines cross or touch it in between.

Never count the shorter segments between two crossing points as separate lines, and never merge two different lines that happen to cross very close to the same point into a single line.

Group the lines in the figure by direction, since parallel lines are the easiest to enumerate without missing or double-counting one.

1. Horizontal lines: the base of the triangle, one horizontal line about a third of the way up, and one shorter horizontal line nearer the top — 3 lines.

2. Vertical lines: two vertical lines drop straight down from the two ends of the topmost horizontal line to the base — 2 lines. Only two vertical lines are drawn in the figure; there is no third one.

3. Lines sloping like “\” (parallel to the right side of the triangle): the right side itself, plus two interior lines running parallel to it — 3 lines.

4. Lines sloping like “/” (parallel to the left side of the triangle): the left side itself, plus two interior lines running parallel to it — 3 lines.

Adding these: 3 + 2 + 3 + 3 = 11.

As an independent check, split the lines into the outer boundary and the interior lines instead: the triangle’s 3 outer sides, plus 2 interior horizontal lines, 2 interior vertical lines, and 4 interior diagonal lines (2 in each slanting direction), gives 3 + 2 + 2 + 4 = 11 as well — the same total.

So the figure contains a total of 11 straight lines.