Fun question:
a12a is a four-digit number with the digit a in both the thousand’s and unit’s places. What is the value of a; if the number is divisible by 6?
Going through the four steps as I would on the test:
What is given?A four-digit number: A12A (it's important to note that A's are DIGITS in a number, and not variables being MULTIPLIED).
I'm also told (as part of the question), that this number should be DIVISIBLE BY 6.
I have a suspicion about what I can do with that.
STEP 2: WHAT IS ASKEDPretty straightforward question here: what is 'a'. I notice, though, it's what IS the value of A and not what COULD BE the value of A. At first this kind of surprised me, as I thought there would be a chance a had multiple possible values. Time to work through using the process I thought of in step 1.
STEP 3: PLAN and STRATEGIZEWell, again, I kind of started doing this in step 1. Knowing that A12A was divisible by 6 means that A must be even: 0,2,4,6, or 8. 0 doesn't work, though, because that would not be a four-digit number! (0s before the first non-zero digit don't count. 0s after the first digit do).
So A is either 2,4,6,or 8. B is already gone.
Knowing that A12A is divisible by 6 *also* means that A+1+2+A = 2A + 3 => must be a multiple of 3 (Multiples of 6 must be multiples of 3, and the digits of multiples of 3 add up to multiples of 3).
STEP 4: SOLVE So which A makes 2A + 3 a multiple of 3? I could plug in the answers and solve (except 3, already eliminated). It's not terribly slow. But if I *really* know my GMAT number properties I know that if 2A + 3 = Mult3, then 2A must be a mult3, and so A must be a mult3.
Only 6 works.
(If I did plug in: 2(2) + 3 = 7, 2(4)+3 = 11, 2(6)+3 = 15, 2(8) + 3 = 19. only a=6 works)
D.