SAT Math

[stiles]

If x is a positive integer, what is one possible value of the units digit of 103^2x after it has been multiplied out.

 

What does that mean?

[Tom Mattson]

It means:

 

If you take this unknown 'x' and put it into the formula 103^2x (I assume you meant it to be an exponent), the result can have which of the following digits in the one's place?

 

When you do SAT Math, the answer choices are just as important as the problems. Post the answer choices and I'll tell you what I mean. This looks like a marathon problem, but I promise you it is not.

[stiles]

Originally posted by stiles

If x is a positive integer, what is one possible value of the units digit of 103^2x after it has been multiplied out.

 

Thanks for clearing that up, so units digit = 1's place. Now I understand it. I calculated 103^2 and 103^4.

 

It ended in 1, and 9, both acceptable answers.

 

Oh, and it was a grid-in question.

[Tom Mattson]

Ah, yes, I should have guessed it was a grid-in question.

 

Originally posted by stiles

I calculated 103^2 and 103^4.

 

I hope you didn't do the full multiplication. There's no need. Check it out. When I multiply the first two digits below, I get:

 

...103

x.103

-----------

......9

 

That's all I need! For success on the SAT, only do as much work as you need to get the answer. That will save you loads of time. ETS deliberately does not give you enough time to solve each problem fully, so if you always do things the long way you will not finish.

[stiles]

Well, I used a calculator.

[Tom Mattson]

:slaphead:

 

I forgot, you get to use a calculator. I also taught courses for the GRE and GMAT, and you don't get to use one there.