It may seem like an odd and specific question, but I'm doing what's currently a Mono-water playthrough of my pokemon sapphire, and I'm thinking of training my Gyarados to level 25 so it can learn Dragon Rage, but I won't bother wasting my time doing that if the Magnemite has over 40 Hp.
Keep in mind, I'm asking about the Magnemite not the Magneton.
Don't bother, Magnetmite's minimum HP at Level 22 with no EVs or IVs would be 43, 3 more than 40.