7 Math Cheat Codes That Feel Illegal

7 mental maths tricks, ranked from useful to "feels illegal" – and WHY each one works, so it's not just magic. Pause at every challenge and try it yourself. Chapters 0:00 97 × 96 in 2 seconds + welcome to Cobbico 0:26 #7 Multiply by 5 1:11 #6 Multiply by 11 2:03 #5 The percent swap 2:54 #4 The digit sum test (divisible by 3 and 9) 4:10 #3 Squaring numbers ending in 5 5:16 #2 Difference of squares 6:11 #1 The near-100 trick 7:50 Recap Challenge answers are in the pinned comment. #math #mentalmath #mathtricks #studytips