Tricky Math

Discus: SAT/ACT Tests and Test Preparation: April 2004 Archive: Tricky Math
 By Justperfect (Justperfect) on Thursday, April 08, 2004 - 06:32 pm: Edit

what is the units' diget of 3^155
a=1
b=3
c=5
d=7
e=9

 By Athlonmj (Athlonmj) on Thursday, April 08, 2004 - 06:36 pm: Edit

Here's a hint:

Find 3^1, 3^2, 3^3, 3^4, 3^5, etc... until you see a pattern

 By Haithman (Haithman) on Thursday, April 08, 2004 - 06:39 pm: Edit

Justperfect aren't you 20 at Yale and scored 1600 on the SAT and told everyone how easy it was to do so?

 By Justperfect (Justperfect) on Thursday, April 08, 2004 - 06:44 pm: Edit

yes but im just giving people practice, espically for you who usally makes careless errors as you said. its just help and practice for you guys.

 By Haithman (Haithman) on Thursday, April 08, 2004 - 06:52 pm: Edit

Well thank you for being so thoughtful. By the way what happened to your last post where I got the one wrong..I cant find it anymore.

 By Justperfect (Justperfect) on Thursday, April 08, 2004 - 07:03 pm: Edit

i'm not sure, but im pry gonna be leaving this board to get back to school.if you want it i can give it to you. good luck studying everyone.

 By Aim78 (Aim78) on Thursday, April 08, 2004 - 07:05 pm: Edit

It goes 3, 9, 7, 1, 3, 9, 7, 1.... .

155/4 = 38 R 3

So I'm going to say the answer is D....?

 By Averagemathgeek (Averagemathgeek) on Thursday, April 08, 2004 - 07:39 pm: Edit

How about factoring out all the 3^4's?
3^155=[3^(4*38)]*3^3=[....1][27]
Therefore, the answer is d) 7.