Problem Solving (PS) | Re: What is the units digit of 9^19 - 7^15?

For cycle questions such as these you simply use division to find the units digit

9 occurs in cycles of 2: 9,1 so you divide the exponent- 19/2 - whatever the remainder is will be the answer - so in this case the remainder is 1 so the units digit will be the first digit in the series "9." When there is no remainder, then the units digit is always the last number in the series. Always start with the number it self- so
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