Advanced GMAT Quant - Page 43 Problem 2

[shaif.ghani]

Hi,

I am having hard time understanding a concept which is discussed in an advance gmat guide.

=> Units digit of (24)^5+2x = Unit digit of (4)^odd. The pattern for the units digit of 4^integer = [4, 6].

Conclusion: "Thus the unit digit of (24)^5+2x is 4".
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I know that the factors of 24 are 4 and 6. The unit digit of 4^integer = [4, 6] and unit digit of 6^integer = [6]. How can you derive the above conclusion that unit digit of of (24)^5+2x = 4, when it could be [4*6=4 and 6*6=6]???

[karthsj]

Hi,

It looks like you have'nt considered one major point,
If Unit digit of (4)^odd then it is either (4)^1 or (4)^3 - both of which gives you the unit digit of 4. hence if the right hand side of the expression is 4, you can conclude that (24)^5+2x is 4.

[shaif.ghani]

Yesss... I missed that... Thanks :)