The 24 + 8 Strategy is actually the 24 + 10 Roulette Strategy but somehow has been represented as a different strategy.
How the mix up in name got started or where the 8 comes from is a mystery. The correct strategy requires a single bet on two Dozens, which is 24 numbers plus 10 straight up bets within the remaining Dozen and a single bet on each remaining Dozen.
If you want to learn about the 24 + 10 Roulette Strategy click here.