Number System : Divisibility by 7
Take the last digit off the number.
Double it and subtract the doubled number from the remaining number.
If the result is evenly divisible by 7 (e.g. 14, 7, 0, -7, etc.), then the number is divisible by seven. You may have to repeat the steps several times.
Lets take an example 4293(say).
step 1: Double the last digit -> 3×2=6
step 2: Subtract it from the remaining number -> 429-6=423
step 3: repeat the above steps to check 423 is divisible by 7 or not -> 3×2=6 ->42-6=36 which is clearly not divisible by 7.
So the number 4293 is not divisible by 7.
Since to check divisibility by 7 is a bit cumbersome process. We can check it by simply dividing the number by 7.
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