There is no scientific basis for these "rules", and they should never be used to "educate" the public about safety. In their book, Essentials of Sea Survival, Golden & Tipton suggest that 50-50-50 rules got their start when someone misinterpreted the 50% "marginal zone" survival curve published by Barnett in 1962.
Four Popular Versions
A person has 5 minutes to swim 50 yards in 50°F (10°C) water and has 50/50 chance of surviving the attempt.
You have a 50-50 chance to swim 50 yards in water at 50°F (10°C).
A 50 year old person has a 50-50 chance of surviving 50 minutes in 50°F (10°C)
If someone is in 50°F (10°C) water for 50 minutes, he/she has a 50 percent better chance of survival if wearing a life jacket.