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If x is a positive integer such that the units digit of x^3
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09 Dec 2017, 16:17
09 Dec 2017, 16:17
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Question Stats:
71% (01:01) correct
28% (00:58) wrong based on 114 sessions
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If x is a positive integer such that the units digit of \(x^3\) is 3, what is the units digit of \(x^{15}\) ?
A. 1
B. 3
C. 5
D. 7
E. 9
A. 1
B. 3
C. 5
D. 7
E. 9
Re: If x is a positive integer such that the units digit of x^3
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27 Apr 2019, 06:33
27 Apr 2019, 06:33
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Given : Units digit of x^3 is 3
To find : Units digit of x^15
Steps to solve:
1. x^15 can be written as (x^3)^5
2. W.K.T, x^3 is 3
3. Now , simplifying step 1 we get, i.e. 3^5 = 243
observe, the units digit here is 3
Hence, the option is B.
P.S. To solve 3^5 quickly, wk.t, 3^2=9
so, 3^5 it boils down to (3^2) (3^2) 3 =9*9*3=81*3=243
Hope, this helps!
To find : Units digit of x^15
Steps to solve:
1. x^15 can be written as (x^3)^5
2. W.K.T, x^3 is 3
3. Now , simplifying step 1 we get, i.e. 3^5 = 243
observe, the units digit here is 3
Hence, the option is B.
P.S. To solve 3^5 quickly, wk.t, 3^2=9
so, 3^5 it boils down to (3^2) (3^2) 3 =9*9*3=81*3=243
Hope, this helps!
General Discussion
Re: If x is a positive integer such that the units digit of x^3
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09 Dec 2017, 19:35
09 Dec 2017, 19:35
1
If x^3 has 3 as unit digit, it must be 7^3 since it equals 343.
The 7 has the following pattern
7 ^1 7
7^2 9
7^3 3
7^4 1
7^5 7 and so one
So 7^15 has a 3 as unit digits. Since I did it quickly, I am pretty sure that it is false. Any help ?
The 7 has the following pattern
7 ^1 7
7^2 9
7^3 3
7^4 1
7^5 7 and so one
So 7^15 has a 3 as unit digits. Since I did it quickly, I am pretty sure that it is false. Any help ?
