Grandpa says: "This is really a stretch but

Prove to me

S = 0.5 or 1/2

Grandpa and his very lateral thinking!

  • 3
    $\begingroup$ Just out of curiosity : Rot13(Znl or vaireg vg naq fnl F.0 = F) $\endgroup$
    – 19aksh
    Aug 8, 2019 at 12:07
  • 1
    $\begingroup$ Clever but I am looking for 1/2 $\endgroup$
    – DrD
    Aug 8, 2019 at 12:20
  • $\begingroup$ Could this have something to do with Shear Stress? Shear stress in fluids to be specific. $\endgroup$
    – Abbas
    Aug 8, 2019 at 12:39
  • 1
    $\begingroup$ No @Abbas. Grandpa is not that engineering minded. Just crazy. $\endgroup$
    – DrD
    Aug 8, 2019 at 12:42

2 Answers 2


Maybe Grandpa starts with


and then (oh no no)

$S = \frac{VI}{IX} = \frac{V}{X} = \frac{1}{2}$ (by treating the letters as products and cancelling the $\small I$'s).

A stretch - but Grandpa's been flexible before: Why would five hundred and five be same as one?

  • $\begingroup$ Bulls Eye! Great Lateral Thinking @Tom $\endgroup$
    – DrD
    Aug 16, 2019 at 11:38

It is possible that Grandpa deduces his claim from

The numbering on the models of the iPhone (listed here)

Explicitly, the iPhone numbering according to generation is as follows:

1st gen - iPhone
2nd gen - iPhone 3G
3rd gen - iPhone 3GS
4th gen - iPhone 4
5th gen - iPhone 4S
6th gen - iPhone 5 (and iPhone 5C)
7th gen - iPhone 5S
8th gen - iPhone 6 (and Plus)
9th gen - iPhone 6S (and Plus)
10th gen - iPhone 7

If Grandpa were to reasonably assume that the model numbering up to this point follows an arithmetic progression, then it would be fair to say that $S$ represents $0.5$ or, indeed, $\frac{1}{2}$. That is, for example, iPhone 5S is really iPhone 5.5

Of course, the progression is broken in the next generation with iPhone 8 but the argument can still be made that if an intermediate version between iPhone $N$ and iPhone $(N+1)$ is constructed then it takes on the numbering scheme iPhone $NS$ which we can reasonably assume to be equivalent to iPhone $(N+\frac{1}{2})$ as it claims a generational position of its own without bias towards its predecessor or descendant.


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