Divisibility (General Rule for 11s)

Last week, we learned how to tell if a 3 digit number is divisble by 11.  This week, we take it to the next level.   

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We know how frustrating long division can be with double digits.  That's why this week, we learn how to tell if a number is divisible by 11 without having to follow all the steps for long division!  To see if a number is divisible by 11, add alternating digits (every other digit).   Then find the difference.  If the difference is divisble by 11 (0,11,22, etc), then the number is divisible by 11.

2728

The first alternating sum: 2 + 2 = 4

The second alternating sum: 7 + 8 = 15

15 - 4 = 11

11 is divisible by 11

therefore, 2728 is divisible by 11!

Ready for some more? Try out the practice problems below!