Question

How to do divisibility by 7?

Answer 1

To determine if a number is divisible 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.
672 (Double 2 is 4, 67 - 4 = 63, and 63 $÷$ 7 = 9) Yes
905 IDouble 5 is 10, 90 - 10 = 80, and 80 $80÷7=11\frac{3}{7}$) No