18 make long calculation easier to read

[Scottan]

Closes #18

n.b. I decided to also expand the help text for this challenge a bit, so that students are more likely to come up with the same (or equivalent) model answer, and made the formatting more consistent while I was at it. Hopefully they should be less likely to get stuck on silly details if they haven't used numpy before and can focus on the important skills this challenge is developing.

[github-actions]

Thank you!

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🔍 Inspect the changes: https://github.com/UoMResearchIT/programming_with_python/compare/md-outputs..md-outputs-PR-87

The following changes were observed in the rendered markdown documents:

 03-numpy_essential.md | 25 ++++++++++++++-----------
 md5sum.txt            |  2 +-
 2 files changed, 15 insertions(+), 12 deletions(-)

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⏱️ Updated at 2026-04-21 14:59:28 +0000

[andrewgait]

Looks good to me - approved.