Write down the first few powers of 2 and look for a pattern in their unit digits.
Can you solve it? How can a unit digit be divided by 9?
Can you check if the answer is 5?
You can check the answer above. I have blurred the answer, and yes it is 5. How do you do it?
21 has remainder 2 when divided by 9.
22 has remainder 4 when divided by 9.
23 has remainder 8 when divided by 9.
24 has remainder 7 when divided by 9.
25 has remainder 5 when divided by 9.
26 has remainder 1 when divided by 9.
27 has remainder 2 when divided by 9.
28 has remainder 4 when divided by 9.
And so on - do you see the pattern? It can be shown that the 5th, 11th, 17th and so on would have remainder 5. 89 is part of that sequence.
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Got ya! thanks