Chapter 5.1, Problem 37E

Here is a divisibility test for 11.

(a) Starting at the left of the given number, add together every other digit.

(b) Add together the remaining digits.

(c) Subtract the smaller of the two sums from the larger. (If they are the same, the difference is 0.)

(d) If the final number obtained is divisible by 11, then the given number also is divisible by 11. If the final number is not divisible by 11, then neither is the given number.

Use this divisibility test to determine whether each number is divisible by 11.

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