Are you really just not good at maths?
That's not a very comprehensive reply is it? Just an insult, really, that doesn't add much to the discussion.
Let's try and shine a bit of light into the shadows here. While, on the face of it, it seems obvious that the ability to form trains form different numbers of carriages to suit the demand is more flexible than being stuck with the multiples of the units you have (in this example 4 car), it isn't actually the case in reality.
Suppose, for example, that a service needs 9 cars on average. Two four car units would be slightly too short, but a 12 car would result in a fair bit of empty space. So a 9 car LHCS seems ideal.
But wait a minute, what about the faff of attaching and detaching small numbers of carriages together? Where would that be done? How many shunters or additional locos would be required for these moves?
As the coaches can't run independently, surely that is a major disadvantage that balances out any numerical flexibility that may accrue?
There is a reason that TOC's prefer running units, and why the LHCS services that run do so, generally, in fixed formations. The reason is financial, and at a time when there is so much focus on cost cutting, having LHCS with its attendant costs is a luxury that we can't afford.
It's also illuminating that it isn't just the UK. European railways have also realised that there is, in fact, little or no flexibility n LHCS, and countries such as Ireland, Switzerland and The Netherlands (the latter two not noted for refusing to invest in rail) have moved, or are moving towards abandoning LHCS workings, and, where they still exist, running them in fixed formations which has no more flexibility than units.
The suggestions that LHCS are somehow how more flexible than MUs however are still nonsensical to me.
You're right. The flexibility is only illusory.