Andrew will be half as old...

[rcude21]

Andrew will be half as old as Larry in 3 years. Andrew will also be one-third as old as Jerome in 5 years. If Jerome is 15 years older than Larry, how old is Andrew?

MGMAT Word Problems Guide pg 21, question 6.

I'm struggling with questions like these where you have to take one-half, double, etc of one variable from the other. Is there a good strategy for knowing what side of the equation (1/2, x2, etc) will go on?

I.e.. A strategy for telling if it should be:
1/2(A+3)=L+3 or
A+3=1/2(L+3)

Thank you!

[jlucero]

Andrew will be half as old as Larry in 3 years. Andrew will also be one-third as old as Jerome in 5 years. If Jerome is 15 years older than Larry, how old is Andrew?

MGMAT Word Problems Guide pg 21, question 6.

I'm struggling with questions like these where you have to take one-half, double, etc of one variable from the other. Is there a good strategy for knowing what side of the equation (1/2, x2, etc) will go on?

I.e.. A strategy for telling if it should be:
1/2(A+3)=L+3 or
A+3=1/2(L+3)

Thank you!

Great question. I've been teaching the GMAT for 4+ years and I still have to double check my math on problems like these. The best thing I've found is to think about which side is larger while I double check my work. For example: "Andrew will also be one-third as old as Jerome in 5 years", in this case, it seems like Andrew (in 5 years) will be YOUNGER than Jerome (in 5 years). So my equation should be:

YOUNGER = 1/3 * OLDER

If I still struggle, I'll plug in some numbers. Let's say Andrew is 10, Jerome is 30. How do I set up an equation to represent that Andrew is younger:

10 = 1/3 * 30
Andrew = 1/3 * Jerome
(A+5) = 1/3 * (J+5)

Obviously the more steps you have to take, the longer it will take you to write out the equations. But especially as you are starting out, take as much time as you need to make sure your equations are written properly.