If n is a positive integer, which of the following CANNOT be the units digit of $3^{n}$ ?

1

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3

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5

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7

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Solution

The correct option is C $5$
The units place of $3^{1}$ is $3$ .
The units place of $3^{2}$ is $9$ .
The units place of $3^{3}$ is $7$ .
The units place of $3^{4}$ is $1$ .
The units place of $3^{5}$ is $3$ .
The units place of $3^{6}$ is $9$ .
The units place of $3^{7}$ is $7$ .
The units place of $3^{8}$ is $1$ .
The units place of $3^{9}$ is $3$ .
Now we can clearly observe here that the units place of $3^{n}$ belongs to the set $3, 9, 7, 1 .$
The answer is option $C$ ( $5$ ).

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If n is a positive integer, which of the following CANNOT be the units digit of 3n ?

If n is a positive integer, which of the following CANNOT be the units digit of $3^{n}$ ?