I first see the magician “Kevin Li” do this. Here’s a link to the trick but if you don’t want to watch it, I typed everything out.
Basically the magician hands his phone to the spectator and lets him enter his birth month and multiply his birthdate then birth year(For example 9x14x1989=250,614). And then the magician asks him to hit the subtract button and let 6 people press six different numbers(phone facing down and the six random numbers were 238,445) so 250,614-238,445 is 12,169. Then the magician lets the spectator pulls out his own phone asks siri how long ago was his birthday. Siri then says 12,169.
Doesn’t looks like a math trick to me but more like an app trick.
Basically the magician hands his phone to the spectator and lets him enter his birth month and multiply his birthdate then birth year(For example 9x14x1989=250,614). And then the magician asks him to hit the subtract button and let 6 people press six different numbers(phone facing down and the six random numbers were 238,445) so 250,614-238,445 is 12,169. Then the magician lets the spectator pulls out his own phone asks siri how long ago was his birthday. Siri then says 12,169.
Doesn’t looks like a math trick to me but more like an app trick.