Spectrum #78: Order these blood types by how common they are — the solution
The Spectrum puzzle from October 31, 2026: six things on one hidden scale, rarest to most common, with every figure and where the checks were best spent.
The puzzle
Order these blood types by how common they are, rarest at the top and most common at the bottom. The board opened in this order:
- AB positive
- A positive
- B positive
- A negative
- O positive
- O negative
AB positive was already in place; A positive opened 3 places from home.
The walkthrough
The ends first. AB positive is the rarest of the six at 3% of people and O positive the most common at 38% of people. Anchor those and the middle four are what is left to place.
Where the scale splits. The widest gap is between B positive (9% of people) and A positive (34% of people) — 25% of people apart. Everything above that line belongs on the rarest side and everything below it on the most common side, so sorting the six into those two groups is most of the puzzle.
The closest call. A negative (6% of people) and O negative (7% of people) are only 1% of people apart — the pair that is a coin flip without the figures, and the place to spend a check: a check locks whatever is already right and leaves only the wrong tiles to swap.
The answer
| # | Rarest to Most common | Figure |
|---|---|---|
| 1 | AB positive | 3% of people |
| 2 | A negative | 6% of people |
| 3 | O negative | 7% of people |
| 4 | B positive | 9% of people |
| 5 | A positive | 34% of people |
| 6 | O positive | 38% of people |
Previous: Spectrum #77 (Fri, Oct 30) · Next: Spectrum #79 (Sun, Nov 1) · All Spectrum solutions
About Spectrum
Spectrum is Noggin’s daily ordering puzzle: six things, one hidden scale, three checks. Tiles in the right place lock green; the figures turn over when the board is done. How to play Spectrum, or play today’s.