PKN wrote:
What is the unit digit of \(1^{1!} + 2^{2!} + 3^{3!} + ... + 9^{9!}\) ?
A. 9
B. 7
C. 5
D. 3
E. 1
This problem tests us on the knowledge of units digit of a number raised to a (positive integer) power. The following is what we need to know:
The units digit of 1, 5, and 6 raised to any power are 1, 5, and 6, respectively.
The units digit pattern of 4 is 4-6. That is, the units digit of 4^odd is 4, and that of 4^even is 6.
The units digit pattern of 9 is 9-1. That is, the units digit of 9^odd is
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