Nice video, just a thing to speed up the process. to quickly find out if a number is divisible by 3, simply add up the digits, so for 149 thats 1+4+9, if the resulting number is divisible by 3, then the initial number is also divisible by 3, so you can see that 1+4+9=14 and 14 is not divisible by 3, but 159 is, because 1+5+9=15 and 15 is divisible by 3. This step can be in theory repeated infinitely and sooner or later you will arrive at 3, 6 or 9, which are the only three 1-digit numbers divisible by 3.
Hi! Yes this is true and there are a few other tricks for other primes as well. I don’t worry about speed too much in my courses - I prefer a consistent method that works every time even if it is slower. but for students taking a timed standardized test the faster tests are great!
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Nice
Nice video, just a thing to speed up the process. to quickly find out if a number is divisible by 3, simply add up the digits, so for 149 thats 1+4+9, if the resulting number is divisible by 3, then the initial number is also divisible by 3, so you can see that 1+4+9=14 and 14 is not divisible by 3, but 159 is, because 1+5+9=15 and 15 is divisible by 3. This step can be in theory repeated infinitely and sooner or later you will arrive at 3, 6 or 9, which are the only three 1-digit numbers divisible by 3.
Hi! Yes this is true and there are a few other tricks for other primes as well. I don’t worry about speed too much in my courses - I prefer a consistent method that works every time even if it is slower. but for students taking a timed standardized test the faster tests are great!