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Which of the following numbers is prime?

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Re: Which of the following numbers is prime?  [#permalink]

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New post 19 Dec 2017, 05:54
Quote:
Hence, the units digit of 4^66 + 7^66 is 5 (6+9).


Tks Bunuel. I understood the cycle power part already but I still don't understand how do we have number 5 here? I mean 4^66 + 7^66 then unit digit of it will be 6+9 = 15 but why it turned out to be 5 (6+9)
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Re: Which of the following numbers is prime?  [#permalink]

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New post 19 Dec 2017, 07:21
lichting wrote:
Quote:
Hence, the units digit of 4^66 + 7^66 is 5 (6+9).


Tks Bunuel. I understood the cycle power part already but I still don't understand how do we have number 5 here? I mean 4^66 + 7^66 then unit digit of it will be 6+9 = 15 but why it turned out to be 5 (6+9)


hi lichting

Can you clarify what you were not able to understand? 6+9 is 15 so unit's digit will be 5 and 1 will be carry forward. so unit's digit of 4^66+7^66 will be 5
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Re: Which of the following numbers is prime?  [#permalink]

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New post 19 Dec 2017, 07:33
niks18 wrote:
lichting wrote:
Quote:
Hence, the units digit of 4^66 + 7^66 is 5 (6+9).


Tks Bunuel. I understood the cycle power part already but I still don't understand how do we have number 5 here? I mean 4^66 + 7^66 then unit digit of it will be 6+9 = 15 but why it turned out to be 5 (6+9)


hi lichting

Can you clarify what you were not able to understand? 6+9 is 15 so unit's digit will be 5 and 1 will be carry forward. so unit's digit of 4^66+7^66 will be 5


I'm so sorry T_T
I thought 5 (6+9) is 5 * (6+9) = 5 * 15.
My mistake. Thank you
Re: Which of the following numbers is prime? &nbs [#permalink] 19 Dec 2017, 07:33

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