Yes, of course you can make $100 a day trading with $100. Just invest $100 to buy a stock that will go up 100% before market closes.
The 3 5 7 rule is a risk management strategy in trading that emphasizes limiting risk on each individual trade to 3% of the trading capital, keeping overall exposure to 5% across all trades, and ensuring that winning trades yield at least 7% more profit than losing trades.