How about we divide 15/3 as it goes completely in 15.. the 15 power will have its unit digit ending as 3.. hence the option is B.

First of all, we can find out that when we multiply the same unit digit, they are following the same law
eg. 23*23=529, 63*63=3969 the unit digit remain the same

When x3' unit digit is 3, and x15=x3*x3*x3*x3*x3
3*3=9, 3*3*3=27, 3*3*3*3=81, 3*3*3*3*3=243,
so the unit digit is 3

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!

I read it the same way as you and solved it the same way too. Thanks for re-assuring this method is the quickest!

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