Hi Tom,

I really dislike this question. No mathematician or user of mathematics would write such an expression. Mathematical expressions are written to clearly state a fact or relationship so that someone else reading the expression will understand it. This expression is meant to confuse you rather than make it clear what is expected.

The convention is that multiplication is performed before addition so you are expected to perform $5 \times 0 = 0$ first so that the expression becomes

\[5 + 5 + 5 - 5 + 5 + 5 - 5 + 0\]

and then the result is 15. The confusion is that you might start from left to right and perform $5 + 5 + 5 - 5 + 5 + 5 - 5 + 5$ and then multiply by $0$ to get a result of $0.$

If I wanted you to perform this evaluation I would write

\[5 + 5 + 5 - 5 + 5 + 5 - 5 + (5 \times 0) =.\]

Your eye is then immediately drawn to $(5 \times 0)$ and you know to perform this operation first.

Harley