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# If n is a positive even integer, what is the probability that the unit

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If n is a positive even integer, what is the probability that the unit [#permalink]

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24 Oct 2017, 22:22
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Question Stats:

46% (01:14) correct 54% (00:54) wrong based on 81 sessions

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If n is a positive even integer, what is the probability that the unit’s digit of $$n^4$$ is 6?

A. 1

B. $$\frac{4}{5}$$

C. $$\frac{3}{5}$$

D. $$\frac{2}{5}$$

E. $$\frac{1}{2}$$
[Reveal] Spoiler: OA

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Re: If n is a positive even integer, what is the probability that the unit [#permalink]

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24 Oct 2017, 22:30
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Option B

When even numbers are raised to power 4 the unit digit is always 6 except when the even number is 10.
Hence sample set is 5 and the desired output is 4

So probability is 4/5

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Re: If n is a positive even integer, what is the probability that the unit [#permalink]

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29 Oct 2017, 06:44
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Expert's post
nkmungila wrote:
If n is a positive even integer, what is the probability that the unit’s digit of $$n^4$$ is 6?

A. 1

B. $$\frac{4}{5}$$

C. $$\frac{3}{5}$$

D. $$\frac{2}{5}$$

E. $$\frac{1}{2}$$

Let’s write out all possible units digits of even numbers:

0^4 = 0

2^4 = 6

4^4 = 6

6^4 = 6

8^4 = 6

Thus, the probability is 4/5.

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Re: If n is a positive even integer, what is the probability that the unit [#permalink]

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30 Oct 2017, 18:10
JeffTargetTestPrep wrote:
nkmungila wrote:
If n is a positive even integer, what is the probability that the unit’s digit of $$n^4$$ is 6?

A. 1

B. $$\frac{4}{5}$$

C. $$\frac{3}{5}$$

D. $$\frac{2}{5}$$

E. $$\frac{1}{2}$$

Let’s write out all possible units digits of even numbers:

0^4 = 0

2^4 = 6

4^4 = 6

6^4 = 6

8^4 = 6

Thus, the probability is 4/5.

But the question says n is positive. So we cant take 0 as a value for n. Also, where does it say that n has to be a single digit number. This seems like a bad question.

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Re: If n is a positive even integer, what is the probability that the unit [#permalink]

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30 Oct 2017, 22:04
Expert's post
1
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gotonishu wrote:
JeffTargetTestPrep wrote:
nkmungila wrote:
If n is a positive even integer, what is the probability that the unit’s digit of $$n^4$$ is 6?

A. 1

B. $$\frac{4}{5}$$

C. $$\frac{3}{5}$$

D. $$\frac{2}{5}$$

E. $$\frac{1}{2}$$

Let’s write out all possible units digits of even numbers:

0^4 = 0

2^4 = 6

4^4 = 6

6^4 = 6

8^4 = 6

Thus, the probability is 4/5.

But the question says n is positive. So we cant take 0 as a value for n. Also, where does it say that n has to be a single digit number. This seems like a bad question.

Jeff there considers the units digits of n, not n itself and not single-digits. So, while n itself cannot be 0, its units digit can, for example n can be 10.
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Re: If n is a positive even integer, what is the probability that the unit   [#permalink] 30 Oct 2017, 22:04
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